A PRE tag is supposed to be rendered verbatim, including white-space. However, when Concordion.NET processes an HTML file, if there is a space or spaces between two SPANs, it gobbles them up.
For example, suppose you have this:
<pre>
<span>X</span> <span>Y</span>
</pre>
If you view the HTML file before processing, you'll see it correctly rendered with a space between the X and Y. However, after processing, the space is gone.