Possible you've found a gtk or oxygen-gtk bug.
If you change gtk style in systemsettings->application appearance->gtk+ appearance to Adwaita or Clearlooks (and restart your session), does the problem persist?
Possible you've found a gtk or oxygen-gtk bug.
If you change gtk style in systemsettings- >application appearance->gtk+ appearance to Adwaita or Clearlooks (and restart your session), does the problem persist?