Dude, I've been playing with the good old Mesh Grabber (not a sexual innuendo). I started working on a character, undressing her (for science, of course) and trying different clothing styles, when I noticed her vagina acting erratically. Well, I then remembered what you went through (still not a sexual innuendo, seriously, guys) and changed tools from mesh grabber to simple node selection tool, and the vagina went back to its original state...Fit control is what I use as well. But sometimes even with large breasts the results are lacking. I need to explore Mesh grabber next. I've been hearing good things about it.
Though no matter how good it is, it won't stop Daz from sucking.
So yeah, if needed, I can confirm that Mesh Grabber is acting the same stupid way...