Code review comment for lp:~alan-griffiths/mir/fix-1335747

To give an idea of the infrequence and scale of the problem here's some output from my investigation:

DEBUG run=188, i=938
DEBUG run=1306, i=662
DEBUG run=5562, i=1444
DEBUG run=12271, i=5
DEBUG run=12604, i=1810
DEBUG run=14656, i=2012
DEBUG run=23680, i=4
DEBUG run=31931, i=474
DEBUG run=35833, i=978
DEBUG run=39250, i=1176
DEBUG run=44260, i=1547
DEBUG run=47337, i=1214
DEBUG run=51397, i=1146
DEBUG run=58659, i=76
DEBUG run=58691, i=8700
DEBUG run=60875, i=1
DEBUG run=70940, i=2093
DEBUG run=75398, i=1137
DEBUG run=80812, i=4
DEBUG run=81348, i=7
DEBUG run=82227, i=94
DEBUG run=83219, i=1424
DEBUG run=90168, i=2145
DEBUG run=90484, i=908
DEBUG run=101722, i=224
DEBUG run=105501, i=1901