UpdatePanel partial update broken by "span" element

I've tested this extensively and scoured the web for anything about it, without any luck.

I have a simple table enclosed within an UpdatePanel.  Some of the table cells issues postbacks when clicked.  Whenever I include any kind of "span" element within any of the cells, the partial page update breaks and I get a full update.

A few hopefully helpful bits:

1. I've used ASP.NET, UpdatePanel and AJAX extensively.  No other problems.

2. There are no HTML errors within the UpdatePanel (nor anywhere on the page).  All controls have unique IDs.

3. The only thing I've found resembling this error online are issues with the LinkButton causing this problem if the ClientIDMode is not set to "AutoID".  This is not the problem here.

Thanks for any help.  If you are interested in this, but need to see more, let me know and I'll grant you access to the resource.