I will attach two testcases. One without non-visible overflow and one with. This might be related to bug 233078 which has a similar description.
*** Bug 286814 has been marked as a duplicate of this bug. ***
Dont know if relevant, but the bug that was duped to this one did not include floats
This is WFM with current trunk build, I can see the bug in Mozilla1.7.
WORKSFORME in Deer Park Alpha 2.