Molicare SuperPlus Leaking?

So a few nights ago I was sleeping in a molicare and I vaguely remember wetting ... at some time later in the night I woke up in a wet bed (definitly not something I wanted)! The thing that really sucked is that it looks like the diaper caught near nothing - it was only wet on the outside (real useful). I was on my stomach when I wet.
Did I get a bad one? Or is there something I should be doing to avoid catastrophic leaks in this situation?

Molicare SuperPlus Leaking?