The new UpdateVersionProperties section in the 4.0 GitVersionTask.targets file is using a different value for FileVersion than the UpdateAssemblyInfo task.
UpdateAssemblyInfo is using AssemblySemFileVer.
UpdateVersionProperties is using $(GitVersion_MajorMinorPatch).$(GitVersion_CommitsSinceVersionSource) in both versions of the targets file.
To maintain consistency with previous behavior, I think UpdateVersionProperties should be changed to match UpdateAssemblyInfo.
I'd be happy to submit a PR if you agree that this should be changed.