Key signature editor missing a snap point

Steps to reproduce bug
1. Create > Key Signature
2. Attempt to drag a double sharp sign to the center line of the staff

Expected behavior: Double sharp sign should snap to the center line

Actual behavior: Double sharp sign snaps to slightly above or slightly below center line.

Discussion: The snapping point for the center line appears to be missing. The snapping point for the spaces immediately right in the middle of the space, Currently the snapping point for the spaces above and below the center line are a little too close to the center line.

MuseScore version: r.2489

(Operating System: Windows XP)