Using MDS on SQLServer 2019/Windows 2019. Database version 126.96.36.199. VS2019 with SSDT.
The presence of a fully qualified view name (master.sys.syslanguages) in one of the MDS stored procedures seems to cause problems when trying to compare the schema and load it into a local project:
udpTransactionSave, line 131:
SELECT @Dateformat = CAST([dateformat] AS NVARCHAR(6)) FROM master.sys.syslanguages where langid = @@langid
Adding a database reference to the master database won't work using Add Database Reference\System Database. As a workaround, I used Add Database Reference\Data-tier Application (.dacpac), pointing to the physical location of the master.dacpac file (not using $(DacPacRootPath) variable), with the option "Same database". This leaves this particular unresolved reference as a warning, but at least there are not dozens of errors that prevent the project from building correctly.
I don't know of any way to submit this as an issue to Microsoft.
This might help others; there was fairly little about this issue online, except the standard "add master database reference", which won't help in this case.