Stylistically, the selection of the ODBC DSN should probably be a radio button rather than a checkbox if only 1 item can be selected.
Not sure what happens in reports that use multiple DSNs though. 
Agreed. Not sure why development did that, but if I had to guess it’s to do with the reuse of the same visual treegrid control. Though I will inquire and get back to you.
When you select the source tables to change in group 2, each of those could potentially be a different connectivity method (ODBC, OLE DB, and even Native) as well as a view, a command object, or even a stored procedure. So if you have multiple tables selected that use multiple ODBC DSNs in your case, what should happen is that the single destination ODBC DSN that you select in group 3 would be changed to for them.
It comes down to the control used which doesn’t support that functionality. We’re investigating replacing it with another control which does offer doing that.
Latest frontend update (Improvements to frontend) now does this. Thanks for your suggestion!