The Exchange Team has completely reviewed and revalidated the Rollup 4 update for Exchange 2010 SP1 and has released an updated version for it. This release includes a fix for the SP1RU4 issue described in KB2581545.
If you already installed interim update KB2581545, then there is no direct need to install this updated release. If you do wish to do so, you must first remove this interim update before applying SP1RU4v2.
If you have not installed the interim update yet but do have SP1RU4 applied to your Exchange 2010 servers, you can directly install the v2 release without uninstalling the v1 release.
SP1RU5 is still on schedule to be released in August.
Download: Update Rollup 4 for Exchange Server 2010 Service Pack 1
View: Description of Update Rollup 4 for Exchange Server 2010 Service Pack 1
View: An Update on Exchange Server 2010 SP1 Rollup Update 4 (background Q&A)