I made tuna mornay tonight, but for some reason, got a weird mess instead of
the nice creamy version I usually make...I use a can of drained tuna, a
small can of drained sweet corn, quantity of cheese sauce, mix together,
place in oven-proof bowl, top with grated cheese and bake for 30mins until
golden on top

the result was a clump of mornay, no apparent white/cheese sauce, and a
watery residue (lots of it)...this has happened a couple of times in the
past, and I've never been able to work out what the problem was, or what
caused it

does anyone know what would cause this phenomenon, and how it might be
prevented?