Thanks for discovering a problem in mtail!
When reporting bugs in mtail behaviour, please be as detailed as possible; describe the problem, what you wanted to have happen, what you observed instead.
If your problem is with the way an mtail program is behaving, please attach or include inline any mtail programs that demonstrate the bug, any log files that mtail was processing, and the observed output.
If your problem is with mtail, please include the commandline you started it with, and the INFO log.
See also Reporting a problem.
Thanks!