Does Send/Receive syncs every email ?

Hello members!

Today lots of GW users in caching mode experienced the following:
After the long weekend users were missing emails between 27 okt and 02 nov. After every send/receive cycle more and more emails appeared in caching mode. Emails were there in online mode. Is this WAD? How can I configure this? Does the client download only few emails in every send/receive cycle?