When right-clicking on a tank with liquid in it with a stack of more than one fluid containers (e.g. bucket) the stack decreases by one, and one bucket's worth of fluid disappears from the tank but no fluid container with that liquid is added to your inventory

Tested with a tank full of water and a stack of 16 buckets

This behavior is also shown in Buildcraft tanks

notes:

Seems like a server/client sync issue, as relogging makes them appear. Something to do with either the inventory methods used (addItemStackToInventory) or editing the inventory at that point in time. Seems to be the former, but I can't work out exactly whats not kicking in.

I'll look into it more later.

I've seen this with Ars Magica I believe, they have meteors right ? GUI desyncs when you place a block near the crash site. So many strange bugs... I know this isn't a helpful comment, just thought it'd be interesting.

Closing this as it's months old. If it needs revisiting we can open a new bug.