@DrJustice and @sevo
I have some good and bad news.
Bad news first: the 50% duty cycle was actually worse with the Pocket Operator - it caused the timing to contract/expand and sort of scatter right through the patterns. This is despite the fact that it seemed to put out a much "cleaner" pulse (it was picked up much easier by my Bastl Klik, for example). I'm starting to get the feeling that the PO's are very finnicky with their clock requirements, as all of these different iterations have worked perfectly to clock my Folktek Mescaline sequencer...
The GOOD news, is that putting scopes onto the initial patch (where I'd added the env/d) actually revealed that the timing of the clock was not changing at all, the envelope just re-shapes the clock into a longer sawtooth (see screenshot with comparison of env/d on top vs the non-env clock on the bottom).
The in-between-good-and-bad is that even though the stop/start clock functionality is great, the clock does not "fire" on the first pulse every time, and seems to fire on the second instead. Actually, it is fairly inconsistent, sometimes firing multiple times on the "1", other times on the immediate upbeat that follows. This means that when I "arm" the PO by hitting it's play button (therefore waiting for a clock from the OP1) and then I hit play on the OP1, they hardly ever start together, as intended.
I'm guessing this to be a phase issue? Does the clock send out an inverted signal, and the pulse is therefore on the downwards slope of the clock (or something)?