Wanderingcowboy

That makes sense. Could be Tweakscale. Didn't think about looking into that mod - I will now. I'll check my other ships that I haven't done anything KAS-wise with yet - could be that using KAS was the coincidence that made me notice. Thanks all for the help!

Long time user of KAS. After putting down Kerbal for a while I just picked it up again - went to my Minmus base and saw that all my fuel lines had disappeared but the ships were still attached. Looked through some forums - KAS had gotten rid of the old JS-1 port (or CC-R2? one of those.) So I uninstalled the mod, downloaded an old version of the mod, loaded an older save, went around disconnecting everything, installed the new version of the mod, great! Now things connect and transfer fuel! ...until I saved my game and reloaded. All my stock fuel tanks now have 283 fuel. The tanks from mods have the right amount, but the S3-14400 tank now only has 283 units of liquid fuel. That's true even when I detach it. This is running KAS 1.5 with Kerbal 1.9.1.