@dsiders
I would gladly test... but using what? The original test.zip for post #1 I assume. Is there a patch or diff with the changes that need to be applied to perform the testing?
1. Download, extract then run attached project
2. Click ten times or so inside the TGroupBox, without clicking another control
3. Click a few times the taskbar(the empty part of the taskbar)
4. Click the TGroupBox again
Repeat 2 -> 4 until you see the issue. As mentioned before, there are other ways to reproduce the bug, but I found the above method the easiest.
Once you see the issue:
1. Open: $(LazarusDir)\lcl\interfaces\win32\Win32WSStdCtrls.pp
2. Go to function GroupBoxWindowProc
3. Add the following lines, just before WM_PAINT:
WM_KILLFOCUS, WM_SETFOCUS:
Exit;
4. Rebuild IDE
The issue should be gone, hopefully without side effects.