When a bundle contains a large number of locales the editor's scroll panes are sized such that no typing can take place in them. I am working on a 1920x1200 display and this is the case even with the IDEA window maximized.
I see at least two JIRA issues reporting this, where the first is flagged as fixed in build #8,931.
I am currently using 8.0.1 #9164 on the Mac, any chance this will be really fixed any time soon? I used to find the bundle editor very useful.