Minor - P4 This code in config_mirrors() is the issue:
explicit_mirror = config_explicit(NULL, "runs.mirror");
if (!explicit_mirror && mmrand(NULL, 1, 10) < 3)
return;
config_off_all("runs.mirror");
This is returning 20% of the time and going on to enable mirroring 80% of the time. This should be the other way around.