If a Rehearsal Mark is a Letter (the default) then the Index should show letters, not the number, etc. That is, the Index displayed in the UI should be the same style as the Sequence type.
I encountered this because (not sure why) the score I am engraving goes from rehearsal mark [I] to rehearsal mark [K] without any [J], therefore, to match the score, I edited the Properties manually to skip [J]. This means modifying the Index to increase the numeric value, whereas, the Rehearsal Marks are using Letters. The Index “should” show ‘J’ which the user can increase, as Letter, to ‘K’ (or vice versa decrease, etc).
Here:
