It would also be very helpful if right-clicking on the non-unique segment would pop up a menu with a list of other instances so the user could easily jump there (the idea is similar to what exists for Matches pane when the same TU is found in several TMX's). Sometimes a non-unique segment calls for an alternative translation, but to be able to examine the context of the other instances you have to use the Search window.
This is implemented in trunk, r6989.
One note: The number of duplicates shown in the context menu and the number of duplicates reported in the search window may differ. The search window does not count a segment as a duplicate if the target text differs, whereas the context menu considers only the source text.
Closed in the released version 3.1.9 of OmegaT.
Didier