possible cause:
-datetime field linked to smalldatetime field or other fieldtype whitch is to small to hold full datetime
-Outlook can change first character of Middle name, Initials etc. to Uppercase. (database value: "van" Outlook: "Van")
-Outlook can add space character to the end of a phone number
-Outlook can remove spaces from phone numbers.(Database value "+31 20 4565423" Outlook: "+31204565423")
-a field is to small to hold whole value, compare during set/get operation will always differ
-Outlook can change formatting of Full Name, Full Address etc. (Upper/Lower case, spaces.)
-Outlook can change values of columns like Owner, LastModifiedTime etc.
-Outlook can reset value of ReminderOverrideDefault column in Calendars