I just started doing battlegrounds over the past few days because my guys just hit 70. I was in a WSG battle where the other side had an abundance of mages. Even though I use a

/castrandom [target=focustarget,nodead,exists,harm] Lightning Bolt,Purge,Grounding Totem

macro on all my toons to ensure Grounding totem is up on every cooldown and buffs are purged, these damn mages were easily able to shoot them all and and one would poly my main. It was the first time I ran into this problem, I targeted the asshat who polyed me and hammered my 'I win' button but it wouldn't go off.

I did notice that when my main was moving around grazing on the bloodstained grass the alts were turning, but I'm sure they didn't actually move enough to break spell casting. So even if my NS was down, they should have started to cast Chain Lightning.

I'd like some more insight on this problem too. I'll keep my eyes open the next time this happens to see if I can observe anymore about the potential causes for the targeting to stop working.