SQL Server 2008 R2 SP2 buildnumber: 10.50.4000.0 or 10.52.4000.0 ?

We have some confusion about the SQL Server 2008 R2 SP2 buildnumber. Could anyone explain why we see both 10.50.4000.0 as 10.52.4000.0? Or is there an intentional difference between the SP2 patch itself (installed updates list in control panel shows 10.52.4000.0) and SQL Server 2008 R2 patched up to SP2 level (both DB properties as SELECT @@VERSION show 10.50.4000.0)?

Thanks, regards,
Lennart Dollekamp