[Win32SS] dropdown-menu position may be wrong, when the window overflows the screen-borders horizontally

0.4.11-RC-34-g5e059e7 gcc dbg linux
I used our rapps.exe for testing here, but the bug is not in rapps, but deeper in ros(Win32SS?). I observed the bug also for other apps, e.g. NirLauncher. I guess every app is affected.

Reproduction steps
-start rapps
-move the window towards the screen border until "File" in menubar is partially offscreen
-expand the rightmost entry of the menubar "help" to make the dropdown-menu appear
-move the mouse to the left, so that each menubar-entry expands
-observe where the left-most "File" menupopup gets positioned

Expected result
-popup-menu is positioned distinctly at the screen border.Easy to reach, nothing cropped
xpsp3.webm

Observed result
-popup-menu is placed wrong and can not be reached easily by moving the mouse
0.4.11-RC-34-g5e059e7.webm

0.4.11-RC-34-g5e059e7.log contains no valuable information (nothing is logged when triggering the error).