I think this might be a result of #6
I don't think it matters, but i'm a frost DK, meaning i get 3% hit from talents.
If i put the statweight for hit and expertise to 0, the calculation will put me under the hitcap, despite the rule being active:

But if put any weight to expertise (not hit!), it works out fine.

It's not really a rule in that sense. The only rule is giving you the highest score, so you need to give hit some value in the first place.

Aah, i see. Me and my guildies were under the impression that it's a minimum. Since you usually want that to kick reliably.

It'll behave that way if you give hit a value above haste. So like 5, for example. That would make the addon try to get you as close to hit cap without going under