I'd love some clarification on this too.
Needless to say, I hate this glitch myself. It does not make any sense at all when a dude can slash someone on the otherside of the door. And it is ridiculous how some people have literally excelled in this glitch. I watch them kill one after another without missing a single time.
Besides, what I have recently experienced with Idzo was the final straw. There I was as a defender behind one of those grid-like doors with square gaps all over (damn, can't remember the map's name). Attackers showed up and started beating it down and I decided to poke them with my great long bardiche through the gaps. And I swear I don't do this. I mean it that I don't. That one single time, I wanted to do it for a change. I mean everyone does it, nobody gets told off, I keep warning people about it all the time, admins seem to have mixed feelings about the issue and the thing gets discussed at least three times on EU2 throughout the day without a conclusion etc. etc. Still, I decided to do it just for once and dear Idzo felt the need to go bossy with me like 'Stop it for your own good'. I explained him quite everything I have written so far and his hero-of-crpg, do gooder bossiness wouldn't back off.
Under the above circumstances, this literally drove me mad. So, all in all, I would seriously like a relevant rule to be introduced and practiced by all game admins. Not that I will even ever try it again in case I have to bear the same shit again but we still need a precise rule here.