Key menu selection in transpose dialog

Steps to reproduce bug
1. Create or open a score (for the sake of discussion assume the key is Bb major)
2. Select a few measures
3. Notes > Transpose...

Expected behavior: When the Transpose dialog opens the key displayed in the drop-down menu should match the key signature of the first measure of the selection. That way it gives a point of reference and makes it clearer that the user is changing the key from Bb major to something else.

Actual behavior: The key displayed in the drop-down menu is always "Cb major / Ab minor" regardless of the current key signature for the selection.

MuseScore version: r. 2649

(Operating System: Windows XP)