findItem and restrictions in EWS code

For those of you Exchange 2007 migrators who wondered why Sumatra needed to put categories in the subject line -- We ran into a bug in Exchange 2007 RTM (Microsoft confirmed fixed in SP1). The same problem showed up in this post involving contacts: http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=1849174&SiteID=17

Basically: you can't use FindItem with restrictions that use SUBSTRING in an EWS XML query:

<restriction>
<t:contains containmentmode="Substring"
ContainmentComparison="IgnoreCaseAndNonSpacingCharacters">
<t:ExtendedFieldURI PropertySetId="00062008-0000-0000-C000-000000000046"
PropertyId="34100" PropertyType="String"/>
<t:Constant Value="mmConv102659080256Z"/>
</t:Contains>
</restriction>

So in contrast to almost every other release Microsoft has done for Exchange -- SP1 actually IMPROVES the migration process! I feel like Fred Sanford expecting to join Elizabeth imminently.