Exactly. Some of the people with checkuser can't be trusted. Answer me this: has AB ever been checkusered? Have I?
I'm sure there is at least one checkuser you trust. Ask them.
The last time I alluded to people with checkuser abusing their power I was told privately to contact the privacy ombudsman. But recent discussion on foundation-l has concluded that the privacy ombudsman has no power over inappropriate use of checkuser, because inappropriate use of checkuser is not a violation of the privacy policy.
Try ArbCom, then (yes, they are much the same people, but I still think you would get somewhere - assuming you have more than just a gut feeling).