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 ([e digicons]-_-[/e] ) and an enemy starbase ([e digicons]8O[/e] ) to use Raze Planet.
It almost looks like they tried to change the "ships stop bombing when scout enters the system" thing most of us came to strongly dislike by bumping up the planet-target priority, but it seems to be a little bit too high!