Version: (using KDE 4.3.1) Installed from: Ubuntu Packages http://techtavern.wordpress.com/2008/08/10/fixing-copy-paste-issues-on-eclipse-and-kde/
sh*** pressed enter per incident. If you use eclipse copy and paste works sometimes not. I googled a while and found the link above, describing the problem and working workarounds quite well.
I confirm this bug is present on KDE 4.3.1 and eclipse galileo
*** This bug has been marked as a duplicate of bug 166606 ***
Turns out it was not a duplicate (of that bug anyway). This is an eclipse bug https://bugs.eclipse.org/bugs/show_bug.cgi?id=153809. It seems to be on it's way to be patched, so that is good. For future reference, the broken gtk function is "gtk_clipboard_set_with_data()" and the working one is "gtk_clipboard_set_with_owner()".