Also noticed that some of the text was not rendering. The solution to this was to find and replace all the font tags.
Find

<Font html:Color="#999999" xmlns="http://www.w3.org/TR/REC-html40">

and

</Font>

and replace with nothing. Not sure if this is a libre office limitation.

I've also had an issue opening xls exports in libre office calc 4.2.7.2. I get a "General Error.
General input/output error" dialog and the export does not display. I had a poke around in the xls file (which is just xml) in a text editor and found in my export the following types of Cell elements were causing the problem:

<Cell ss:Index='2' ss:StyleID=&#x27;story-color-0&#x27;>

I did a search and replace in the file, replacing &#x27; with ' so that you get:

<Cell ss:Index='2' ss:StyleID='story-color-0'>

I could then open and view the file in libre office. Looks like an encoding issue with the export function.