Right, I think I know how to solve this one now, or at least how to get into the final stage of solving it. But I think the pushers in the Eastern section might still be bugged?
Continued below (spoilers)
It's possible I'm triggering things in the wrong way, but in the screenshot below I end up like this — the vertical pusher isn't able to push the horizontal ones up any further, which prevents them from vaporising in the black hole.