Not very often, but often enough to mention...

One of my toons will cast their Lightning Bolt at a target that my current main is not targeting.

I'm using:

#showtooltip Lightning Bolt
/assist [target=party1]
/cast Lightning Bolt

For the most part the slaves will always cast at the master's target. Does not matter which toon the master is, as long as that toon is the party leader.
Occasionally, they will pick a nearby target other then the master's and attack that one instead.

Yesterday in Zul'Farrak, I was nuking a troll and one of the alts (with identical macro's to the other three who were on target) decided to nuke a scarab instead.

Has anyone else encountered this? Is there a fix for it?