There are quite a few changes made in mr4mp2 but what really depends is the issues that you are facing is that fixed.
Some common issues like
Proactive Threat Protection displays the status "Waiting for Update" after a client migration
Windows Security displays the warning "MALWARE PROTECTION out of date" after a user manually runs an Active Scan or a Complete Scan
Clients cannot download content from Group Update Provider (GUP)--This was a major issue
During installation of LiveUpdate, lucheck.exe returns an invalid error code
Ping response times increase in releases since Symantec Endpoint Protection 11 MR3
Inconsistent behavior with NTP "Microsoft Windows Networking" settings---Used to block network shares
Deleting old packages generates errors in the Symantec Endpoint Protection Manager during manual LiveUpdate
Slow process of DAT files in the Inbox\Agentinfo folder on the Manager
- But i am still not sure if it is completely fixed
And many more which you can check in the release notes for sep
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007121216360648