The window selection mode doesn't work anymore in Windows Version 1809
It just selects the whole screen or parts of the task bar.
Windows 10 Version 1809
I updated today, didn't plan to yet but I wanted to try to reproduce this issue.
Unfortunately I cannot, Greenshot seems to work as usual.
I am still update 2 other systems, maybe one of them has the behavior you are describing...
But if you have any additional information which might help, please let me know!
I just tried again. Now everything works fine.
Weird, I didn't restart Windows or Greenshot in the meantime.
I tried several times on different windows before.
I think this can be closed then. Sorry for any inconvenience caused.
No problem, glad it works.
I think there was an application with a gigantic invisible overlay on your screen, whatever the reason...
If you encounter it again, check what applications are running.
Enjoy your Windows 10 1809!