[tor-relays] Rendezvous on non-OR circuit?

I've been running a tor relay for several days now (C65EF5E06B8338CF976D376048BE2C8FBD499C9C). During my regular checks I noticed something odd within the tor log files.

[WARN] Tried to establish rendezvous on non-OR circuit with purpose Acting as rendevous (pending)

It occurs several times per hour and I couldn't find anything except the [bug tracker](https://trac.torproject.org/projects/tor/ticket/15618) which seems to be outdated (newest message is four weeks old).

I'm concerned that this could be some kind of "attack" that could compromise users, as I'm running an exit node. Does somebody have more information on this matter?