zlib compression bomb warning in notices.log on a middle relay

Multiple users starting from at least 0.4.4.5 and further (0.4.5.1-alpha) have some warning concerning zlib compression bombs. Here is an example from one of my relays (I have the same on all my relays)

Nov 02 05:30:55.000 [warn] Possible compression bomb; abandoning stream.
Nov 02 05:30:55.000 [warn] Possible zlib bomb; abandoning stream.
Nov 02 05:30:56.000 [warn] Possible compression bomb; abandoning stream.
Nov 02 05:31:00.000 [warn] Possible compression bomb; abandoning stream.
Nov 02 05:31:00.000 [warn] Possible compression bomb; abandoning stream.
Nov 02 05:31:00.000 [warn] Possible compression bomb; abandoning stream.
Nov 02 05:31:55.000 [warn] Possible compression bomb; abandoning stream.
Nov 02 05:31:56.000 [warn] Possible compression bomb; abandoning stream.

I don't know if it is a new feature of Tor or if this is an ongoing attack. I'll also mail the tor-relays@ ML in order to see how many people are affected.