matplotlib · yushuosun · Sep 8, 2026 · Sep 9, 2026
diff --git a/lib/matplotlib/backends/qt_editor/figureoptions.py b/lib/matplotlib/backends/qt_editor/figureoptions.py
@@ -7,6 +7,7 @@
 
 from itertools import chain
 from matplotlib import cbook, cm, colors as mcolors, markers, image as mimage
+from matplotlib.patches import BoxStyle
 from matplotlib.backends.qt_compat import QtGui
 from matplotlib.backends.qt_editor import _formlayout
 from matplotlib.dates import DateConverter, num2date
@@ -251,8 +252,48 @@ def apply_callback(data):
             if axes.legend_ is not None:
                 old_legend = axes.get_legend()
                 draggable = old_legend._draggable is not None
+                bbox_to_anchor = old_legend._bbox_to_anchor
+                bbox_to_anchor_kwargs = {}
+                if bbox_to_anchor is not None:
+                    # Keep the same bbox anchor and transform.
+                    bbox_to_anchor_kwargs = {
+                        "bbox_to_anchor": bbox_to_anchor._bbox,
+                        "bbox_transform": bbox_to_anchor._transform,
+                    }
+
                 ncols = old_legend._ncols
-            new_legend = axes.legend(ncols=ncols)
+                new_legend = axes.legend(
+                    loc=old_legend._loc,
+                    ncols=ncols,
+                    numpoints=old_legend.numpoints,
+                    markerscale=old_legend.markerscale,
+                    scatterpoints=old_legend.scatterpoints,
+                    borderpad=old_legend.borderpad,
+                    labelspacing=old_legend.labelspacing,
+                    handlelength=old_legend.handlelength,
+                    handleheight=old_legend.handleheight,
+                    handletextpad=old_legend.handletextpad,
+                    borderaxespad=old_legend.borderaxespad,
+                    columnspacing=old_legend.columnspacing,
+                    mode=old_legend._mode,
+                    fancybox=isinstance(
+                        old_legend.legendPatch.get_boxstyle(),
+                        BoxStyle.Round,
+                    ),
+                    shadow=old_legend.shadow,
+                    title=old_legend.get_title().get_text(),
+                    title_fontproperties=old_legend.get_title().get_fontproperties(),
+                    frameon=old_legend.get_frame_on(),
+                    framealpha=old_legend.legendPatch.get_alpha(),
+                    edgecolor=old_legend.legendPatch.get_edgecolor(),
+                    facecolor=old_legend.legendPatch.get_facecolor(),
+                    linewidth=old_legend.legendPatch.get_linewidth(),
+                    alignment=old_legend.get_alignment(),
+                    prop=old_legend.prop,
+                    **bbox_to_anchor_kwargs,
+                )
+            else:
+                new_legend = axes.legend(ncols=ncols)
             if new_legend:
                 new_legend.set_draggable(draggable)
 

diff --git a/lib/matplotlib/tests/test_backend_qt.py b/lib/matplotlib/tests/test_backend_qt.py
@@ -218,6 +218,95 @@ def test_figureoptions():
         fig.canvas.manager.toolbar.edit_parameters()
 
 
+@pytest.mark.backend('QtAgg', skip_on_importerror=True)
+def test_figureoptions_preserves_legend_settings():
+    from matplotlib.backends.qt_editor import figureoptions
+
+    fig, ax = plt.subplots()
+    ax.plot([0, 1], [0, 1], label="line a")
+    ax.plot([0, 1], [1, 0], label="line b")
+
+    old_legend = ax.legend(
+        loc="lower left",
+        bbox_to_anchor=(0.1, 0.2, 0.3, 0.4),
+        ncols=2,
+        numpoints=2,
+        markerscale=1.5,
+        borderpad=0.9,
+        labelspacing=0.6,
+        handlelength=1.8,
+        handleheight=0.9,
+        handletextpad=0.7,
+        borderaxespad=0.3,
+        columnspacing=1.6,
+        mode="expand",
+        fancybox=True,
+        shadow=True,
+        title="Legend title",
+        frameon=True,
+        framealpha=0.4,
+        alignment="right",
+    )
+    old_bbox = old_legend._bbox_to_anchor
+
+    def form_values(form):
+        values = []
+        for label, value in form:
+            if label is None:
+                continue
+            if isinstance(value, (list, tuple)):
+                value = value[0]
+            values.append(value)
+        return values
+
+    def fake_fedit(datalist, **kwargs):
+        general = form_values(datalist[0][0])
+        general[-1] = True
+        payload = [general]
+        if len(datalist) > 1:
+            payload.append([form_values(curve[0]) for curve in datalist[1][0]])
+        if len(datalist) > 2:
+            payload.append([form_values(mappable[0]) for mappable in datalist[2][0]])
+        kwargs["apply"](payload)
+
+    with mock.patch(
+        "matplotlib.backends.qt_editor.figureoptions._formlayout.fedit",
+        side_effect=fake_fedit,
+    ):
+        figureoptions.figure_edit(ax)
+
+    new_legend = ax.get_legend()
+
+    assert new_legend._loc == old_legend._loc
+    assert new_legend._ncols == old_legend._ncols
+    assert new_legend.numpoints == old_legend.numpoints
+    assert new_legend.markerscale == old_legend.markerscale
+    assert new_legend.scatterpoints == old_legend.scatterpoints
+    assert new_legend.borderpad == old_legend.borderpad
+    assert new_legend.labelspacing == old_legend.labelspacing
+    assert new_legend.handlelength == old_legend.handlelength
+    assert new_legend.handleheight == old_legend.handleheight
+    assert new_legend.handletextpad == old_legend.handletextpad
+    assert new_legend.borderaxespad == old_legend.borderaxespad
+    assert new_legend.columnspacing == old_legend.columnspacing
+    assert new_legend._mode == old_legend._mode
+    assert new_legend.get_alignment() == old_legend.get_alignment()
+    assert new_legend.shadow == old_legend.shadow
+    assert new_legend.get_frame_on() == old_legend.get_frame_on()
+    assert new_legend.legendPatch.get_alpha() == pytest.approx(
+        old_legend.legendPatch.get_alpha())
+    assert new_legend.legendPatch.get_linewidth() == pytest.approx(
+        old_legend.legendPatch.get_linewidth())
+    assert list(new_legend.legendPatch.get_facecolor()) == pytest.approx(
+        list(old_legend.legendPatch.get_facecolor()))
+    assert list(new_legend.legendPatch.get_edgecolor()) == pytest.approx(
+        list(old_legend.legendPatch.get_edgecolor()))
+    assert new_legend.get_title().get_text() == old_legend.get_title().get_text()
+    assert new_legend.prop == old_legend.prop
+    assert new_legend._bbox_to_anchor._bbox.bounds == old_bbox._bbox.bounds
+    assert new_legend._bbox_to_anchor._transform == old_bbox._transform
+
+
 @pytest.mark.backend('QtAgg', skip_on_importerror=True)
 def test_save_figure_return(tmp_path):
     fig, ax = plt.subplots()