The problem maybe to do with the floor not being
right up against the bottom of the bowl.

Over time and use the same thing MAY happen.

Make sure the floor is nice and level. If there is
any wiggle room, shim it and get it right.

In the case that I had in my home, I shimmed it, screwed
it down CAREFULLY and used the same sanded grout
(that I used on the floor) to squeeze around the bottom of the bowl.
Let it dry for a few days and its rock solid!

It'll be a slight pain in the ass to remove down the road, but
with the way its installed I should never have to.

Tom