We're getting closer. Now I have to compare some statements and see if I get the full picture:
We have created the appropriate Setting Container
If you named it "appropriate Setting" this would be useful, but as I doubt that's the case: Please remember that Technical Support requires Technical Details at all times. No assumptive replacements. (Yes that was a bit of sarcasm, hoping that sinks in for the next time you post

)
Please post the exact name of the Setting Container in question along with All the Other Settings for the setting container in you created for this feature.
the container choice will not save.
Your "Modify DID" setting does not change, or your "container choice" does not save? Unclear.
What options are you presented with and what URL are you at? And which option do you choose (we already know that your choice is changed to "disabled" upon submit. But I'm not clear if you mean the Modify DID page or the Settings container page and I like to be 100% sure before I look. Also I've noted that others often chime in when all the information is avaiable and I am suddenly redundant. Which I don't mind at all. LOL