Can reproduce using the UIMA tutorial.
1) Open RoomNumberAnnotator.xml
2) Go to Capabilities tab.
3) Double click RoomNumber type to edit.
4) In the Edit Types to a Capability Set, click anywhere in the grid outside the Input / Output cell columns (e.g., click RoomNumber in TypeName).
5) A dialog appears telling you to click in the right columns.
6) Try clicking OK in the dialog and another appears.
7) Repeat 5-7 ad infinitum.
Have to quit Eclipse at this point to get out of the loop. Same thing happens in the Add/Edit Features dialog too.