I finally set up the packet capture that I should have done months ago. 
Code:
proxy=http%3A%2F%2Fwww.fast-web-proxy.Cn%2F&hint=http%3A%2F%2Fwww.fiveproxy.cn%2F&cat_id=51&email=sdgs@epwing.com
d'oh! It's looks like out block code is case sensitive.

We didn't see this, because we convert the data to all-lowercase before we save it.
We need to swap the order of those functions...
I know that I tested this in the past, so this bug was introduced in some changes we made.
More darkly humorous: It's actually impossible to enter uppercase characters into the domain blacklist.
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