I had another customer that used a cover over hers for the first couple of weeks. I don't know why, but sometimes the bamboo needs wearing in alot more for some than others, and it could be as you say ..... if he wees a large volume all at once, the bamboo might just not be worn in enough to cope with such a large amount of wet.
I would expect them to just keep on improving, but let us know how you get on