I think this can actually happen with any illusion, and isn’t a new behaviour. In the past it’s been quite rare. I think if an illusion decides that it does not have a path to attack its actual target it will pick a different one.
For example, at the champion wurm in TA (before today’s patch), I’ve summoned a warden on top of the champ, and after the usual staring contest where the warden does not attack, it ran off and attacked one of the silver wurms.
