That's interesting.... the exact same thing happened to me once. Only mods I had installed were the RCM (pretty sure it was 1.8.5) and the most recent iteration of Partyswap. Didn't play around with KSE or anything, so I have no idea what could've caused such a thing, and I haven't been able to replicate it since
Roth: what are you playing on? Steam, Steam updated, GOG, etc?