It can happen, despite the brake drums being of generous proportions. Sometimes, it can be caused by parking the car up with the handbrake on with hot brakes (eg after some spirited driving)
At this stage though I'd be tempted to check the replacement cylinders and shoes. As TMG says check the cylinder is free to move in the slot and has been lubricated with a little HMP grease.
Also check the brake linings, especially if you have the bonded on type. Had a set of non Mog ones from a reputable maker with a large pocket between shoe and lining which gave rise to a high spot between lining and drum.
Arwyn
