SSMS 2012 and LocalDB problem: can't edit or create new diagrams

OK, yesterday I installed SMS2012 and got it to work with LocalDB (installed 4.0.2 update for .NET 4, etc, etc). All good. System is Win 7 x64, also with VS 2010 + SP1, system is fully up-to-date.
I created new diagram in a database, save it, all good. But now when I want to modify that diagram (or create a new one) I get following eror:

=================================== Attempted to read or write protected memory. This is often an indication that other memory is corrupt. (SQLEditors) ------------------------------ Program Location:    at Microsoft.SqlServer.Management.UI.VSIntegration.Editors.ISqlVirtualProject.CreateDesigner(Urn origUrn, DocumentType editorType, DocumentOptions aeOptions, IManagedConnection con, String fileName)    at Microsoft.SqlServer.Management.UI.VSIntegration.Editors.VsDocumentMenuItem.CreateDesignerWindow(IManagedConnection mc, DocumentOptions options) ...