We shouldn't have to live with this anymore. To me Vanish was put into the game for exactly this reason, so assassins could finally take somebody out and get away without being caught. If we're required to put 5, 15, 35 points into an RA it should work properly. I'm sick and tired of of programmers taking the short cut with coding just so they can say the problem is fixed. It honestly can't be that hard to flag just PBAE spells to continue without a target.
FYI this was also reported by Mythic as a bug many moons ago in a Grab Bag. When they last tweaked stealth and casting. They said they were aware of the issue and that it was a bug. This needs to be fixed.