Now, I had tried it earlier and noticed something looked fishy.  Now I
can reproduce the problem:

1. With an active region, call C-M-%
2. Switch from the minibuffer back to the original buffer
3. Call keyboard-escape-quit (maybe twice) to quit the minibuffer
   prompt.

Then the buffer-local value of `isearch-filter-predicate' is not cleaned
up.  Is it by any chance intentional that minibuffer-exit-hook doesn't
run in this case?