In reply to James Jackson:
aye, snow under the mechanism was the first suspect; but it was happening far too often even after a thorough cleanout.
I was suspecting either:
the mechanism is sensitive to the tolerance it's made by (it's only just held in by design), and/or,
going steeply up hill was moving the unit (given it's 10mm flex travel) enough to make the think pop (it was only really happening going up steep and uneven ground)
only happened once on Sunday; which was major improvement over every 5 min on Sat......
I'v not fully looked over the mech to understand how it works, so I don't know how, or what, was pinging out of place.
as a side note; (in skin mode) I managed to get a fair bit of lateral heel movement, about a good 1", on an icy traverse:
The toe wasn't 100% locked; it looked like it was, but the lever was just short of fully cranked up. (ice in the lock slots)