I got the drum off, its very wet in there, and the cylinder was popped open at one end. The bit of the shoe that the cylinder acts on was bent, is that normal with popped cylinders?

Jesus, you did stamp on them didn't you! Did you suffer a visit from the incredible hulk?

Joolz and Louise,
that's something which I've never seen, yet...

Tbh, the only way I can think of it happening was if the shoe wasn't fitted correctly, or the retaining clip through the backplate was missing, which might allow enough offset between the tip of the shoe and the brake piston to initiate buckling.
If the lower pivot was seized, that wouldn't help much either.

ken

No, but it may very well be normal with brakes that have been assembled by an inebriated chimp in the dark.

Look, I promise, I never touched them.

I was suprised, because the shoes do seem fairly hefty.