On Build Configuration page, if you click "edit" button it allows you to change settings on all available tabs - Plan Details, Source Repository, Builder Configuration, etc. You can switch to any tab and make changes. If you switch back to can see the the changes are still preserved. However, if you click save button, only changes in the current tab will be saved. Changes in other tabs are lost.

For example, if I change Builder JDK in Builder Configuration tab to some other value then switch to Source Repository tab and click save, the change I made is reverted back to the original.

I am not sure is this the expected behavior or a bug. But in my case, it is quite confusing.