Bug. The Change Connection functionality within the SQL Editor is disabled by SQL Source Control.
When my connection is disabled in SSMS, I use the Change Connection functionality to reestablish it. With SQL Source Control installed, I can't because the Change Connection functionality is disabled.
AdminChris Auckland (Admin, Redgate) commented
This doesn't seem to happen for me with SSMS 2012 (11.0.2100.60) and SQL Source Control 3.0.13
The button is disabled if the SQL Source Control tab is in focus, but so are all the other query related buttons. If I have a query window in focus the button is still enabled for me. Does the button become enabled as soon as you uninstall SQL Source Control?