When running an ExecutionEnv, we don't want to be clearing the selection state after the run - we need that state for when reselect() is called on the env.
Fixes #5560 (closed) (at least, the newer version of the symptoms in that bug)
Poking @joneuhauser if you have time to look at this, because I'm undoing something you added in commit 66a4a644, and I might not have full context.
But it seems to me that callers of ExecutionEnv expect to be able to re-apply the selection that was present at run time.