A follow-up note Tobias. It seems we narrowed down the problem to the <br />
tag. This break tag appears in the code when I change a line with ENTER in a cell.
example:
<a href...></a><br />
<div>...</div>
A cell containing this is ignored by the filter in Opera.(break tag written with a space)
<a href...></a><br/><div>...</div>
This works normally in Opera (break tag without a space)