Say I have a stack of PRs waiting for CI. I want "Merge when ready" on the stack. The problem is, that if I enable it on all PRs in the stack, then it seems to immediately enqueue any downstack PRs that pass CI checks first. If I don't enable merge when ready on them, the top PR won't merge the stack when all checks are complete, defeating the purpose of the feature. Am I misusing or misunderstanding something here? It would be nice to have an atomic "merge stack when ready" capability.

what you're seeing is expected. if you enable it for the stack, each downstack PR will merge as soon as it's ready.