Problem with SIP (SNOM phone?)

I recently got a SNOM 300. Works fine, but I notice ongoing messages in the log like this:

Nov 4 10:13:56 DEBUG[23729] chan_sip.c: Stopping retransmission on ‘5446a6f6053de6b1516bdbdd0c4866ea@’ of Request 102: Match Found

When I tried restarting asterisk (and said ‘gracefully’ instead of ‘now’), my session was dropped, but asterisk kept running - apparently it thought there was a SIP call ongoing. Had to hard-kill the asterisk process. Any idea what is causing these?