Hey Tim,
I take it by "CRN" you mean the product key, correct? If this is the case then, yes, you're correct -- putting a product key in the "email" field will return the product key. This is a previously undocumented feature, which we've now documented.
The FindPKey function behaves like the search box on your product version page -- that is you can search for either an email or a product key and LimeLM returns the result.
Or, in short: not a bug, a feature. 😉