Troops shooting each other during planet invasions? That was ages ago. The tutorials must be out dated.

What happened was is that one animation screen was replaced with another. If memory serves me right, this change occurred during the release of the Twilight of the Arnor expansion. There should be no problems with this. The rules governing planetary invasion are the same as it was when the game was first released.

I suggest that you attack with fleets of invasion ships (Hopefully with more troops than what the target planet has). Have high soldering (higher than your opponents preferably). Use planet invasion tactics (be mindful of the ones that can cause the planet quality to drop).