Can't change multiple note velocities

This may be Mac-specific. In 2.0.0 and both earlier betas.

In a manuscript such as the enclosed excerpt, whose history involves MIDI import from another (non-xml -compliant) (deceased) application, where all of the notes have been assigned "user" velocities via that process, I want to edit them all to "Offset, 0", so I can control dynamics properly.

When I select a note, then right-click "Select all similar elements", either using a selection or not, then FN-F8 (inspector), the "velocity" input box is recalcitrant: I cannot erase the first digit, and if I try the up-down control at the side, it seems to hear me, but immediately thereafter restores the value. This makes it nearly impossible to accurately wash a whole score of note velocities.

At least on the Mac (Yosemite). Repeatable on the enclosed excerpt (although I've had it continuously). Thanks!