This is a stopgap measure, I don't know if the underlying issue is fully understood - but this prevents it from happening in the given test case.
By overriding the base for the pocket prism, which is a trick also applied by
TopoShape::makeElementPrismUntil() if the prism creation fails on first try, the bug where said prism goes to the wrong shape is avoided - this on its own would however break a pad in the inverse case, so we only do that when pocketing
594010d9f0