I am having the same issues with my CT3900 in DOS. Dune2 changes the mixer the same way as well. I suppose you have a Creative sound card, too. Then try another version of Creative Basic Utilites. If my memory serves, I switched to mixerset 2.18, aweutil 1.36 etc. This -partially- solved the problem. I mean if you experiment with the different volume levels, you can find a combination which stucks. Far from perfect, it might work and help with keeping your speakers intact and spare you from a heart attack.
"Ita in vita ut in lusu alae pessima iactura arte corrigenda est."