we also got this problem
see my post :
http://forums.quark.com/t/15012.aspx
3 different situations can occur :
- when text insert cursor is INSIDE the font field of the spec window and doing "Apple" (Command key) + D (or B or ....) at the same time
- when saving the doc (very hazardous)
- when playing around with Suitcase (see my post)
so far : no explanation , no solution