FxCop: Compound word should be treated as discrete term

FxCop wants me to spell Username with a capital N (i.e. UserName), due to it being a compound word. However, due to consistency reasons we need to spell it with a lowercase n - so either username or Username.

I've tried tweaking the CodeAnalysisDictionary.xml by adding the following section to the section:

<DiscreteExceptions>
  <Term>username</Term>
</DiscreteExceptions>

From what I understand how custom dictionaries work, this should tell FxCop to treat username as a discrete term and prevent the CompoundWordsShouldBeCasedCorrectly (CA1702) check to fire an error.

Unfortunately this doesn't work. Does anybody have an idea why that is and how to solve this? I don't want to add suppressions, because this would seriously clutter the GlobalSuppressions file as there are quite a lot of occurrences.

Edited to add: For the time being I have solved this by using GlobalSuppressions, but given the nature of the issue this doesn't seem like the ideal way to solve this. Can anybody give a hint on where to look for further information on how FxCop applies the rules defined in a dictionary?