The problem described below occurs on trunk builds. It does not occur on branch-2.4 and branch-2.5 builds.
1. Install a simple cluster (HDFS+YARN+ZK is enough)
2. On the UI, go 'Admin' --> 'Stacks and versions' --> Select the 'Versions' tab --> Click on the "show details" link --> click on the editor icon
3. Change one of the repo url's to a different but valid one
4. Press save
5. Nothing happens. If you uncheck the "skip validation" checkbox, then the repo is sometimes saved.