[Avid-L2] Blanking issue rendered into dissolve remnant of the old DV setting?

I'm trying to remember an old issue that would crop up when something in the render settings that effected video when working with DV footage 720x480 instead of 720x486.  I forget if it was in the render settings where you can choose render same as source or was it a project setting.  This behavior is cropping up on some dissolves and not others.  Re-rendering eliminates the black bar at the top of the screen.  I'm pretty sure this is a HD project and wondering if some edit station was somehow set to whatever that force DV processing like setting?  Got the fix but trying to speculate the cause.

John Moore Barking Trout Productions Studio City, CA bigfish@pacbell.net