Meiannatee's post in Dual Cab Block Cab 2 Reset When Changing Cab 1 was marked as the answer
It's not a bug. The dual cabs is treated as 1 block in helix. When changing cab 1, you're changing the whole block to a new one.
When you change cab 2, you're changing a parameter in the same block determined by your cab1.
To have helix treat cab 1 and 2 separately, use 2 single cabs in parallel paths. DSP usage is the same (i think)