Just had a game where there was a Swiftblade who would sit and farm lanes solo and when we'd try and gank he'd immediately start a TP and then Blade Fury, making him invul to stun. We had no aoe stun so it was basically pretty lame. In the end he got to farm like crazy and carried his team to victory as he was around level 22-23 geared up like crazy when we were all 14-17.
Is this a bug? Shouldn't activating BF cancel the TP?
I know that in DotA, a common strategy for Juggernaut is to BF and then TP/boots out when the team goes for a gank on you. That may have been what he did.
AoE stuns don't go through magic immunity... don't know what you guys are on about. Unless this occurs in HoN, though I haven't noticed it happen. It certainly doesn't occur in DotA. And yes, spin+TP is a legit escape mechanism. Remember that it costs him valuable farming time as well as 135 gold, so you can just count it as a successful gank.