Bc2000 (for the BCF2000 & BCR2000)

How embarrassing ... 
The Roland XVs, Fantoms, SonicCell and the Yamaha Motif XS (didn't check my Motif ES rack) can all change in real time via sysex. Filter frequency sweeps on held note work perfectly well.

Looks like the problem in my studio is just the EMU P2k series and the Yamaha FM gear as well as my forgetful brain.
Alan Currall tells me that the Ensoniq SQ80 also has this problem.

So perhaps your AN1x is OK.

Royce (brain dead from too much coding of old synths)