I'm having a repeated issue when editing two bundle .properties files (right-click => open). When i try to "remove property" (remove a bundle key on both files), NetBeans freezes and uses 25% CPU without stopping. For information, my .properties files are 1346 lines each.
I'm not able to reproduce this issue with more then 3k line in two files - no slowness at all. If the issue still occurs in your setup please attach slowness report and reopen the issue.