SSIS Doesn't keep changes in properties

I’m needing to create 3 versions of an SSIS 2012 solution, dev, prod, and test. The only difference between the three is that any connection manager that points to a database needs to point to its corresponding database.  So the prod OLE DB connections need to connect to the prod data base, test needs to connect to test, etc.  I copied the solution folder and contents to get 3 copies. I change the database names in the appropriate places.  Save the file.  When I reopen, they are back to the original values, changes are not saved.  How to make the changes hold?

I see other people on the web reporting this problem.  I don’t understand the responses they are getting.

Thanks,

Cipriano