Bug: Waveform Preview in bus is sliced off if FastBounce is off

Excellent animation by SquireBum says it all, here:
 
http://forum.cakewalk.com...-confirm-m3556565.aspx
 
 
To reproduce:
1. A project with two audio tracks going to one Master bus.
2. Turn on the Waveform Preview button in the Master Bus and press Play. The waveform should be drawn as expected.
3. Now select the audio tracks and go to Files->Export Audio and DESELECT FAST BOUNCE.
4. Start the Export.
 
As the export progresses (at playback speed, of course) there is a thin horizontal black line being drawn in the Master Bus track and the rendered preview waveform is cut off above this line.