Another example of a similar issue:
When you use WinSCP, open a file in the editor and then do CTRL+F, the search screen will open on top of the WinSCP screen, not grouped, same coordinates, in exactly the same size as its parent window.
It does get weirder though. If I exclude the WinSCP.exe, the search window will then start grouping itself to the (by the looks of it) highest z-ordered window capable of grouping. Only when I ungroup it by dragging it away, the search window will open the normal way. Until WinSCP is started again, than it starts this 'auto-grouping' behaviour again. (This happens whether or not WinSCP is also excluded from the real auto-grouping.)
Running Windows 10 and Groupy RC 1.15.