Continuing this as a monologue ...
Did a test this morning. New session, 2 stereo audio tracks.
Audio 1: - Insert A: Dyn3 De-Esser multi-mono, unlinked (DSP)
- Insert B: MDW 3.0 multi-mono, linked (Native)
Audio 2: - Insert A: Dyn3 De-Esser multi-mono, unlinked (DSP)
- Insert B: MDW 3.0 multi-mono, unlinked (Native)
Save and close session.
Reopen session, and now it looks like this:
Audio 1:- Insert A: Dyn3 De-Esser multi-mono, unlinked (DSP)
- Insert B: MDW 3.0 multi-mono, linked (Native)
Audio 2:
- Insert A: MDW 3.0 multi-mono, unlinked (Native)
- Insert B: MDW 3.0 multi-mono, unlinked (Native)
The problem only appeared on Audio 2, and this time, the duplicated plugin was the unlinked MDW itself (with the same settings as the other one).
On Audio 1, with the linked instance of MDW, there was no problem; no plugin substitution.
So .. seems maybe this is being triggered by unlinked multi-mono instances of MDW? Or somehow in combination?
Note that I have also attempted this with unlinked Channel Strip (DSP) in place of MDW, and it too copies over the instance of the De-Esser above it. I then tried putting an unlinked Softube Saturation Knob in place of the D3 De-esser, and it got written over by a copy of the Channel Strip plugin below it as well ..
It seems unlinked multi-mono is the problem here.
-Dave
edit: I have now tested this on earlier versions and 4 different Mac-based rigs, including non-HDX PT10 ... The behavior is consistent.