Ubuntu 12.04 (64bit): Select, then copy/paste not working

[windozer]

In Windows, I was able to do copy-paste operations. I can select a region of the image, then choose 'copy' and paste it somwhere else in the image. However, in Ubuntu 12.04, these functions are not working. When choosing 'copy' or Ctrl-C and 'paste' or Ctrl-V, then nothing happens. Same goes for 'cut' or Ctrl-X.

[xnview]

This feature is not yet implemented on XnViewMP