Odd serialization problem

This may not be BizTalk specific at all, but it's a problem I've run
into while working in BizTalk... so, I'm posting in this newsgroup as well.

I'm using the RetrieveAs method on a message part to deserialize the
message to an object. From what I know, this method ultimately using
the XmlSerializer to generate the object. The object was generated
using the xsd command line tool and therefore also contains
"XXXSpecified" boolean fields that indicate whether a specific field was
actually specified in the incoming xml.
On one computer, these "Specified" fields are filled in correctly - they
are set to "true" when that field (or corresponding xml element) exists
in the input message.
However, locally, those "Specified" fields aren't correctly populated.
And I have no idea why. I've used the exact same code on two different
computers - it works on one, but not on mine. The major differences
between the two computers are:

Other computer:
- Windows XP
- .Net Framework 2.0.50727.832


Local computer:
- Vista Ultimate
- .Net Framework 2.0.50727.312

I couldn't find any details about changes in the framework updates, but
could that be the problem? Was there some blatant change in it? Or am
I missing something else in my BizTalk configuration?

-Mark-