Screen freeze

[rikona]

Geeqie is a nice tool I use when looking through a photo
collection. Occasionally I will set it to full screen mode. If I then
try to go to another desktop via ctl-alt-arrow, the screen freezes in a
way that I can't seem to recover from. The full screen photo stays
there no matter what I do.

I'd appreciate any suggestions for recovering from this. Running 16.04
Ubuntu, fully updated, with several KDE pgms also.

Thanks...