I would not really class this as bug but in the interests of 100% validation...

If the product description starts with a <p> tag and the truncated text loses the closing </p> it will fail validation.

I added an extra function into function zen_trunc_string to check for unbalanced p tags and add one on the end if necessary which seems to be working ok.

(Why do I have a p tag in the product description anyway? - I use <p class... to style the first paragraph differently,)

Steve