It's quite possible there's a bug that's cropped up with the temperatures. I'll recheck that they're operating as expected.
Just to be clear, it's currently designed to work like this. Certain bodies have a defined starting temperature (like Earth), so the planet enters the simulation as what you expect to see, not a molten wasteland, or an ice ball.
If it's using the generic handling, it will automatically find the instant temperature of the body, based on it's distance to the surrounding stars. (As if it had been there long enough to stabilize), In a simulation with no stars. The body will come in at 0 kelvin (-273.15)