[TYPO3-RTE] Why is a zero a   in a table?

[Daniel Doesburg [netcreators]]

I made a table in the RTE(htmlarea 1.1.1) and filled it with 1, 2, 3 -- 
9, 0, 1, 2 and so on.
But the cells with zero's stay empty!
In the RTE it stays a zero. But in the page it's a  .

What can be a reason?

Regards,

Daniel