This is relatively similar to questions such as these:
How can I change my default database in SQL Server without using MS SQL Server Management Studio?
https://superuser.com/questions/364825/sql-server-management-studio-ignores-default-db
That being said, Management Studio is ignoring all the suggestions. I'm logging in as sa, and I can see that the default catalog for sa is being changed successfully, but Management Studio ignores these changes in the dropdown:

Even if I change it to specific_database_name, and even if I can look at the sa login Properties menu and see that it's set to specific_database_name, Management Studio will always default that combo box to master.
I've tried:
Exec sp_defaultdb @loginame='sa', @defdb='specific_database_name'ALTER LOGIN sa WITH DEFAULT_DATABASE = specific_database_name- Going into the Properties menu for login sa in Management Studio and setting it in the dropdown box there.
The OP in the second question eventually fell back to using a batch file to log in as a different user, but I'd personally just rather keep having master show up. Also he did mention being able to set this on the connection properties themselves, but it's greyed out on my system, and I seem to remember being able to set this for an individual user a long time ago on another machine.
How can this be set? Note that this is not using a Windows login, but a SQL Server one instead. Thanks.