On the course homepage, the following code is used to center the jump menu:

<div align="center" class="jumpmenu">

This is invalid XHTML. To fix, replace the above code with:

<div style="text-align: center;" class="jumpmenu">

Or better yet, remove the align attribute and add the equivalent CSS declaration to the jumpmenu class.

The fix need to be made on line 329 of: /course/format/lams/format.php