Attribute being replaced - I'm completely mystified

[kjkrum]

I have a program that uses XPath to drill down into a DOM-parsed XML Document and extract attributes from the elements. It's worked great for a long time... or so I thought. Today I discovered that these two XML elements were giving me me a really strange problem: the "expr" attribute of the second element is being replaced by a fragment of a different Rule element from elsewhere in the file.

This is not happening to any of the dozens of other Rule elements in my input file. If I comment out the first of these two elements, the problem disappears. Even stranger, it disappears if I add an empty comment before or between these two lines!

<Rule expr="{LD}(\(?{SECTOR}\)? \&gt;{NL}? )+\(?{SECTOR}\)?" event="cimCoursePlot"/>
<Rule expr="{LD} *{SECTOR}( +{SECTOR})*" event="cimSectorInfo"/>

What in the world is going on here?!