Clickonce IsFileGroupDownloaded bug

Question

We have a filegroup in our clickonce deployment that is optional, contained in the file group are some dll's that are not directly referenced by our project and rarely get updated, they are copied into our projects output folder via a nuget package that just injects content files.

Downloading the filegroup when needed works great.
Future runs of that application version also works great, IsFileGroupDownloaded returns true.
However when we updated our application but did not change any files in the file group IsFileGroupDownloaded returns false and it redownloads them.

The [documentation][1] says this:

If a new version of the application has been installed, and the new version has not added, removed, or altered files in the file group, IsFileGroupDownloaded(String) returns true.

However this does not appear to be the case. I did a diff against both version's manifest - the only changes were the application version and the digest of our core application dll (this is what I updated).

Why then does it say that the file group is not downloaded?

A very similar question was asked before and never answered (from 2008 https://social.msdn.microsoft.com/Forums/en-US/910e76ce-d1a2-478c-8f3d-80d736ccb7a6/isfilegroupdownloaded-bug?forum=winformssetup) [1]: https://learn.microsoft.com/en-us/dotnet/api/system.deployment.application.applicationdeployment.isfilegroupdownloaded?view=netframework-4.6.2