The `flush()` method sets `_active.flag = True` without first checking if it's already set. Unlike `add()` which guards with `if getattr(self._active, "flag", False): return None`, `flush()` unconditionally sets the flag and proceeds. If `_flush()` triggers a GC warning that routes back through the logging integration to `flush()` (instead of `add()`), the nested `flush()` will execute, and its finally block will set `_active.flag = False` prematurely, leaving subsequent re-entrant calls unprotected.