Its not bannable, I would post you screenshots from a GM confirming its not bannable, but everyone knows by now that its not. Plus im not at my PC
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This is simply a spot that the aggro range of the guards doesnt cover, its not like the guards see you but cant reach you because you are abusing some roof. On top of that, there shouldnt be guards at all at current patch in lhc afaik, but thats not handleable on a 12k population server, hence the loop hole that allows you to pvp still seems perfect. Would add way more guards once naxx arrives.
Cheers.