Colony changes hands

I landed a colony ship on a nice little 15 rated world. A few turns later I checked in. My colony is now in the hands of a Pirate Group. No notice, no warning -- poof, it's gone. All your colony now belong us.

I sent a ship over to investigate; there was no Pirate ship in the area. When the ship I sent would have contacted the colony -- it vanished. I suppose it too is now under control of the Pirates. I rage quit.

This morning I decided to find out if anyone knows how and why the change was sudden and what can be done about it.