Oh!
You sprayed after you applied pastel chalks? I did that on an armor model about a year ago and have never done it since. Although I didn't get the "frosting" at that time, all my weathering was gone...vanished...disappeared. That's when I learned that except for a few specific applications, you never over-spray pastels after they are applied.
You may have a reaction between the solvents in the Dull Cote and the pastels. I'm not sure. However, it's another possibility thrown into the equation.
Also another thought...Is any of your base paint thinned with alcohol? If so, it may have not been completely dry (all the way through).
Let me know how things turn out. (Also, you can probably get away with adding a light top coat after about 24 hours...it won't hurt anything.)
Enjoy your modeling...