Fabfilter Plugin only works with Generic UI

[Ross93]

I'm having a very strange bug, and I think it's reaper related.

I've got a fabfilter plugin on a track and it's working, but when I use the fabfilter UI, the sound doesn't update... however if I switch to the generic UI and touch one of the sliders, then the sound updates the way it's supposed to.

Switching back and forth, I can see that generic gui and fabfilter gui are in sync = when I change one, the other changes too... but the SOUND doesn't change until I touch the generic gui slider.

I'm using the latest version of reaper.