release will fail if there is change merged.

sbt 'release with-defaults' will check if there is any change in upstream branch, well before release we do build and test, there might be new change merged to upstream branch, and then release will fail. 
If we disable 'pushChanges' in build.sbt, it will not check upstream branch but the 'NextVersion' will not be pushed.  
How to deal with this race condition ? 