In the UI, hovering over interfaces tells you where the reported value differs from the desired one. This should also appear in the error message (and log) when a user attempts to setup a network and fails due to out-of-sync.
verified on: 4.2.5.2_SNAPSHOT-82.g16813b0.0.scratch.master.el7ev 3.10.0-862.6.3.el7.x86_64
This bugzilla is included in oVirt 4.2.5 release, published on July 30th 2018. Since the problem described in this bug report should be resolved in oVirt 4.2.5 release, it has been closed with a resolution of CURRENT RELEASE. If the solution does not work for you, please open a new bug report.