This is seems to come from the LDAP Policy value: MaxValRange
"MaxValueRange controls the number of values that are returned on a single attribute on a single object.
Default"1500
Hard Limit: 5000"
-- http://ldapwiki.com/wiki/MaxValRange
To fix this:
Go to the domain controller that we’re connecting to for the sync
Find the file ntdsutil.exe (most likely under c:\windows\system32 or c:\winnt\system32