Tor clients warn when they use the wrong ntor onion key

I got this warnings (exactly once, for the first time I'm aware of) on my 0.2.4.16-rc bridge on Windows.

Strangely I found no tickets for any of these failures.

Aug 31 09:37:10.793 [Warning] onion_skin_client_handshake failed. Aug 31 09:37:10.793 [Warning] circuit_finish_handshake failed. Aug 31 09:37:10.794 [Warning] connection_edge_process_relay_cell (at origin) failed.

I'm unsure what _client means. Did my client (yes, I use my bridge's client functions) fail or did the client of an connecting bridge user fail?

Client functionality is not affected.