Major Description
If multiple error events are logged against the same SMTPAppender/Manager at the same time, one email will contain both error messages, while the second will be empty (no events).
The original SMTPAppender patch included synchronization against the CyclicBuffer to prevent such simultaneous access from multiple threads. This appears to have been lost in the merge/refactor. Patch (to follow shortly) re-introduces synchronization against the CyclicBuffer in the narrowest possible scope.