Tesco White bread mix.
Dough placed in Loaf tin and covered with cling film and allowed to rise.
Top slightly above edge of tin. Remove Cling film.
Placed in preheated oven for appointed time.
When done top of loaf is well above edge of tin.
A "groove " runs the length of the loaf which has come from the edge of the tin.
When looking at the face of the loaf the groove continues and when allowed to cool and then cut
The top splits from the slice that has been cut.
Can some kind person tell me why this should happen and how do I avoid it