Description of the Bug Report
The new and simplified subwindow code for dragging it added a new bug that makes the OpenGL/Vulkan subwindows inside a group that is resized, not refresh properly.

To Reproduce
N/A

Expected behavior
No redraw issues and subwindows to appear properly.

Screenshots

In this video, the subwindows move properly, but the timeline with the thumbnails has refresh issues and leaves garbage behind (part of the timeline window):

FLTK Version
1.5 GH

Operating System / Platform:
Ubuntu 25.04

Linux/Unix Runtime, if applicable:

• Wayland