gochan's test failure

[Mario Domenech Goulart]

I noticed a failure in gochan's tests today: ​http://salmonella-linux-x86.call-cc.org/master-debugbuild/gcc/linux/x86/2017/11/26/salmonella-report/test/gochan.html

-- testing timers: each gochan-tick gets consumed by only one recv -----------
10ms messages for 105ms means 10 messages ............................ [ FAIL]
    expected 10 but got 12
    (length results)
hopefully different senders: (1 1 1 1 1 2 3 3 4 4 4 4)
1 test completed in 0.124 seconds.
1 failure (100%).
0 out of 1 (0%) tests passed.
-- done testing timers: each gochan-tick gets consumed by only one recv ------

I've never seen this one before. I'm reporting in case it can help to spot a difficult to reproduce issue.