Crash in MySQL backend protocol

During tests with mysqlslap running against the current develop branch, MaxScale crashed with a segment fault:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffc8dfa700 (LWP 11944)]
0x00007fffc81e25ae in gw_read_backend_event (dcb=0x7fffbc00c000) at /usr/local/skysql/maxscale/MaxScale/server/modules/protocol/mysql_backend.c:455
455 CHK_SESSION(session);

This suggests that the session pointed to by the DCB passed to gw_read_backend_event was freed during processing. Unfortunately, I was looking for other things and did not gather any additional diagnostic information. The problem does not readily repeat.