A common problem I have when applying a dissolve in or out of a matte or a fill, is that I often get a slight, but noticeable dip to black on my video.  Even with the proper amount of heads and tails, I still get this dip to black.    

Anyone else come across this problem?  

put a collapse (submaster) effect on your matte and fill and then add the dissolve.

I think you have to map that button from the command palette to either a button somewhere or to you keyboard.

 That is correct. When you want to make a clean global transition from a multi-layered effect stack to a single clip (or vice versa) always use the collapse function, or you will see the slight dip to black you describe because filler material is also part of the dissolve from uncollapsed layers.

 thank you!

 You're quite welcome. We're all here to help.