Help! Fizzy Cake!

xxdeebeexx

Hi, I regularly make my own cakes.... usually a victoria sponge mix -
8oz marg, 8oz caster sugar, 4 eggs 8oz SR Flour

and this is put into an oblong pyrex roasting dish to cook...

up until the last couple of times it has been great.

Last time it tasted/felt as if the SR flour still had some of the raising agent in it as it seemed to fizz in my mouth and at the back of my throat.

It is normally eaten within a day, by my teenage boys, but this hung around for nearly 3 days which makes me think that the boys weren't keen on it either.

Any ideas what might have gone wrong?

tia

dx