I had the same issue with a freshly installed and updated daily build from July 20th, but it turned out the issue was already reported as bug #1026066 (https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/1026066). However, this may not be the same issue you are having.
I had the same issue with a freshly installed and updated daily build from July 20th, but it turned out the issue was already reported as bug #1026066 (https:/ /bugs.launchpad .net/ubuntu/ +source/ software- properties/ +bug/1026066). However, this may not be the same issue you are having.