A little workaround
 

For whatever this is worth to someone, I found a way to avoid getting those damn red clips when I switch from one Vegas project to another.

I first click on "New" and then select the next project I need to open from there. It takes almost no extra time, whereas switching directly from existing project to existing project required switching to a third project and then back to the second one, or closing Vegas 9.0c down and reopening.