Well that was odd....

[Sunsparc]

I pushed my fuel depot into Munar circular orbit last night (around 115km) and when I came back an hour or two later, the apoapsis had climbed up to 300km. RCS and engines were off.

The only thing I can think of is the fuel was unbalanced and it was rotating a bit, but that shouldn't have caused it.

Weird.

[Sol_Rokks_Teddy]

why did you leave your game running for an hour or two? Do you have any mods installed? I hear that quantum struts can cause some phantom forces, as can part clipping.

[Sunsparc]

No quantum struts on this particular vessel, though I believe some parts are clipped.

I walked off for a few minutes which turned into longer, I normally don't leave the game running all the time like that.

[Tw1]

Otherwise, you may have inadvertently discovered a way to increase orbital energy without any power?

It would be cool to see someone use this to get from Kerbin to the Mun. hint, hint.

[NeoMorph]

God.. the phantom forces... If the phantom force was in the prograde direction I could see it doing that...