I am at the end of my tether with the 2-pack of microwaveable 0+ dummies by MAM!!
They keep developing bubbles in the plastic at various points & eventually become unusable because the plastic bulges where my LO would have it against his face.
At first I thought it was me:
- that I was getting water inside it (so i stopped submerging it in the water when cleaning it);
- or the microwave was the problem (its not - is 800w & dummies can be done at up to 1000w);
- or I wasn't putting enough water into the box (I am definitely filling it to the line!)
Plus, sometimes a newer pack of dummies will develop bubbles whilst an older pack is fine (for a while anyway!)
Or they'll be fine for a short while & suddenly start getting bubbles.
It just makes NO sense & I literally have a pile of 7 dummies that have been rendered unusable. I wrote to MAM & they were great - I got a pack sent out but this developed bubbles after the 2nd sterilisation!! 
I'd love to know if anyone else has had this happen or if it really is just me.