Black background for unloaded data area

We found this bug during the WiNGS workshop but cannot reproduce constantly.

Most likely it was related to 'Clamp to View' and 'Lock Track Height(Pixels)', as one time we loaded the 2 tracks from attached bookmark:

1. Lock one of them
2. Select Clamp to View
3. Unlock the one in step #1
4. Lock the other track
5. Unselect Clamp to View
6. Zoom out

Then we observed the unloaded data area background changed to black (originally gray).

Please play with these 2 tracks on lock & clamp to see if you reproduce this bug constantly.