So in the terminal, I mount a camera connected by USB, mkdir a new dir, cp some photos, open that dir with Thunar and I can see them as thumbnails. Then I go back to the Thunar window later and go to close it with the X on the top, and it says:
This window might be busy and is not responding.
Do you want to terminate the application?
(It's possible that after transferring the pictures, the camera is automatically going to sleep at some point, but the directory showing in Thunar is the copy on the hard drive, not the mounted directory on the camera card.)
So I click no, then minimize it. Then I maximize it again a bit later after unmounting the camera, and now it's showing a black blank window that still won't respond. I had something similar recently too, but it didn't do this in the past with the same procedures and same hardware.
could be a lot of things. Sounds like it is hung up making thumbnails