I don't know if this is a bug, and I have a workaround, so its not really a problem, but I am really puzzled by this behavior - here's the issue:
I created a simple new program with a single sawtooth oscillator. Everything is at the default state.
I added a Rez LP Filter to the layer by clicking on the "FX" tab. I wanted to modulate the cutoff with an envelope. So I right clicked on the "Filter cutoff" knob, and assign it to a new AHD envelope at the layer level.
Returning to the Edit tab, I cannot for the life of me get that AHD envelope to do anything with the cutoff frequency!
If I change the modulation source to an LFO (at either the layer or the program level), no problem, the cutoff is modulated as expected. Same with an external MIDI controller, all works fine. But the envelope does nothing, and I tried assigning the envelope at both the layer and program levels.
Just to make sure I was applying the AHD correctly, I turned off the Layer level effect, and returned to the edit window. I then added a Rez LP Filter in the Keygroup(s) panel of the modulation section. This assigns the filter at the keygroup level, as one might expect. I assigned that to the AHD, and voila, it works as expected!
Since I can get the filter modulation to work at the keygroup level, I have a workaround, but I can't figure out why I couldn't modulate the cutoff the original way I tried doing it. I initially suspected a hierarchy problem, but the LFO (assigned at either the program or layer level) works at the layer level just fine, so I am stumped.

Any ideas?