Clipboard functions under kde apps or gtk+ (gnome)

i’ve noticed that actually (maybe only in my installation) the copy/paste to/from system clipboard actually doesn’t work: i can’t copy a text section from say gedit (or kwrite is the same) and paste it into a juce TextEditor, nor i can’t do the opposite. the strange fact is that actually the clipboard is working normally in any other app… anyone can confirm it is working (so could be my mistake) ?