Vst Pitch Slide (91 Xxyy) Alters Dsp Values?

This is with the latest 5.1 Alpha 4

I’m not sure if this a bug or something that I’ve simply overlooked.

I have 1 track with one note (VST string synth) that plays for half the pattern and then pitch-slides down using the 91 panning column pattern effect. This is fine, but I notice that the mpReverb effect I have in the DSP effects dialogue has had some of it’s values over-written and automated. In particular, the Duration field has been highlighted for automation, even though I have specified no automation envelopes.

Is this because certain pattern effects overwrite attributes of some effects? I can manually create an automation envelope to overwrite what’s happened but I’m a little confused. Should I post a screenshot?