The issue is not with colonizing exclusively. I launched a TEC game last night and built a Marza w/ Raze Planet. Jumped into an enemy system, and the Marza made a beeline for the planet, ignoring an enemy capital ( ) and an enemy starbase ( ) to use Raze Planet.
I think this bug is specific to ANY ability that has to do with cap ships and planets. I got my lvl 6 egg and it imediately wanted to suck the planet dry of an enemy when I jumped in, even though the auto-cast is turned off.