If you are using M-S base and DuPont clear, you may be fighting yourself. THere is no guarantee that the two will merge correctly. I've not had problems with loss of adhesion when using different manufacturers products together, but I've only done it on my own stuff. I don't like to get to gutsy when working on a customers vehicle. I have used both DuPont and M-S products over the years, and honestly, am not at all impressed with either, but that's neither here nor there. You're problem seems to be mostly gun adjustment and technique. Mixing products should be something you refrain from, at least without doing your own testing. Now that you've had this problem, you maybe know what NOT to do.
Metalshaping & Kustom Paint