I just tried what you described, but I can't confirm it. I assigned only factories to the home planet until all available spaces were filled. It then automatically returned to the first factory I placed and the Buy button had lit up. I know I've never had to go to the next planet and back again, as I've always simply clicked another square on the planet's map, then selected the particular improvement I wanted to buy. I'm running Beta 2A.

Yes, I doubleclick on the improvement to get it to plop the improvement down and then it automatically moves to the next available tile. This only places the improvement, it doesn't auto-buy it. And I stand corrected about it automatically coming up with a lit Buy. This time when I tested it, it cycled back to the first one placed with an option to Demolish. I then had to click on the desired tile itself to get the Buy light to appear. However, I'm fairly certain you can do all you need to do while you have the particular planet's map up, without having to cycle to the next planet in the list and back again.