You should file your problem in issuetracker, and maybe put in those links I mentioned above. They may be related somehow.
BTW, you can rightclick the manifest file and select "Show in Explorer" and open it in a notepad. Change it there. Restart AS, and reopen the project. This was one of my tricks to comply with this situation. It worked most of the time.In the latter link above, there is a suggested workaround, you could try that one also.