Hello Caroline Jaensch,
The false behavior when trying to resolve the decimal types again in the reverse mapping wizard is fixed with the latest internal build. If you download and install it you should not be experiencing such problems anymore.
Unfortunately, I am not able to provide you with an exact time frame when the SQL Server 2008 types will be supported by Telerik OpenAccess ORM. They are on our TODO list though.
All the best,
the Telerik team