Steps to Reproduce

1. I run winform application under windows. when I copy chinese characters into Textbox. the Exception occured.
2. for example chinese characters:测试， Ctrl+C then Ctrl+V into textbox.
3. stack trace , below:
   System.ExecutionEngineException: String conversion error: Illegal byte sequence
   encounted in the input.
   at (wrapper managed-to-native) System.Runtime.InteropServices.Marshal.PtrToStr
   ingAnsi(intptr)
   at System.Windows.Forms.XplatUIWin32.AnsiToString (System.IntPtr ansi_data) [0
   x00000] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System.Window
   s.Forms\System.Windows.Forms\XplatUIWin32.cs:933
   at System.Windows.Forms.XplatUIWin32.ClipboardRetrieve (System.IntPtr handle,
   System.Int32 type, System.Windows.Forms.XplatUI+ClipboardToObject converter) [0x
   0008d] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System.Windows
   .Forms\System.Windows.Forms\XplatUIWin32.cs:2893
   at System.Windows.Forms.XplatUI.ClipboardRetrieve (System.IntPtr handle, Syste
   m.Int32 type, System.Windows.Forms.XplatUI+ClipboardToObject converter) [0x00000
   ] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System.Windows.Form
   s\System.Windows.Forms\XplatUI.cs:575
   at System.Windows.Forms.Clipboard.GetDataObject (System.Boolean primary_select
   ion) [0x00039] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System
   .Windows.Forms\System.Windows.Forms\Clipboard.cs:390
   at System.Windows.Forms.Clipboard.GetDataObject () [0x00000] in D:\j\workspace
   \build-package-win-mono\2018-06\mcs\class\System.Windows.Forms\System.Windows.Fo
   rms\Clipboard.cs:137
   at System.Windows.Forms.TextBoxBase.ProcessKey (System.Windows.Forms.Keys keyD
   ata) [0x000a4] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System
   .Windows.Forms\System.Windows.Forms\TextBoxBase.cs:1101
   at System.Windows.Forms.TextBoxBase.WndProc (System.Windows.Forms.Message& m)
   [0x0003e] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System.Wind
   ows.Forms\System.Windows.Forms\TextBoxBase.cs:1495
   at System.Windows.Forms.RichTextBox.WndProc (System.Windows.Forms.Message& m)
   [0x00000] in D:\j\workspace\build-package-win-mono\2018-06\mcs\class\System.Wind
   ows.Forms\System.Windows.Forms\RichTextBox.cs:1191
   at System.Windows.Forms.Control+ControlWindowTarget.OnMessage (System.Windows.
   Forms.Message& m) [0x00000] in D:\j\workspace\build-package-win-mono\2018-06\mcs
   \class\System.Windows.Forms\System.Windows.Forms\Control.cs:228
   at System.Windows.Forms.Control+ControlNativeWindow.WndProc (System.Windows.Fo
   rms.Message& m) [0x00000] in D:\j\workspace\build-package-win-mono\2018-06\mcs\c
   lass\System.Windows.Forms\System.Windows.Forms\Control.cs:209
   at System.Windows.Forms.NativeWindow.WndProc (System.IntPtr hWnd, System.Windo
   ws.Forms.Msg msg, System.IntPtr wParam, System.IntPtr lParam) [0x00085] in D:\j
   workspace\build-package-win-mono\2018-06\mcs\class\System.Windows.Forms\System.W
   indows.Forms\NativeWindow.cs:240

Current Behavior

Expected Behavior

On which platforms did you notice this

[ ] macOS
[ ] Linux
[ ] Windows

Version Used:

Stacktrace

Please paste the stack trace here if available.