Double tags when putting list in text block

When I put a list in a text block, everything works fine, but when I change and save the page again, an extra ‘layer’ of

and

tags is added to the items. This keeps repeating, zo after three saves, the code of two list items looks like this:

<ul>
<ul>
<ul>
        <li>first item</li>
</ul>
</ul>
</ul>
<ul>
<ul>
<ul>
        <li>second item</li>
</ul>
</ul>
</ul>  

Only solution for now looks like going to the text view of the text block and manually delete the double tags.

Is it a bug? A browser problem? Are you familiar wit the problem?

Thanks for the support,

Sytse