Cornstarch for you Americans.
I've found a starch thickened sauce or soup kept in a bain marie for a long sometimes splits.
This usually happens when its been there for a few hours or longer. Not supposed to keep them there for longer than 4 hours but our bain marie's at work are on all day and get changed halfway through service which is about 5 hours each way.
It usually happens with leek and potato and mushroom soup, say if its been made without a roux and the cornflour was added just to adjust the consistency of the potato soup. We sometimes use a starch thickened white sauce which can split as well.
Just made me wonder if anyone else had discovered this before