I don't know if that can help, but I have orbital decay around Minmus right now at 12700meters above sea level, 32km AP (and rising) and 8500m PE (and falling at about 15m/s), but it STOPS when fast forwarding. I've just decoupled my ship, and the two "ships" still suffer from it (A stayputnik with a communotron 16-S, a Z-100 and a OX-STAT. On the other ship a TD-12, a Mk1 "Tin can", a Mk16-R, a HS-125, a TD-12, an AE-FF125, two CBS-125 (containing a Z-200, a RGSCM-01 and aASCM-b), a FT-T400, a FL-T100 and a LV-909)
Edit: I want to add that when I left 4x zone (The height where you can timewarp at 4x max), the decaying instantly stopped