A customer currently running an older version of an app experienced an error after successfully upgrading the software: Could not load file or assembly Microsoft.Xaml.Behaviors. However, this assembly was not referenced explicitly anywhere in the codebase, through Nuget or namespace in wpf xaml or code behind or Directory.Packages.props. It might be a transitive dependency, but I used asmspy in the output directory and got no results for dependencies on this assembly. I cannot reproduce this error, every time I rebuild and reinstall the software System.Windows.Interactivity.dll is correctly placed in the output dir, which is the expected behavior.

Someone mentioned that local environment settings may cause the code that references Interactivity:

<Window
...
xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity">

...

<i:Interaction.Behaviors>
    <shared:ApplicationItemViewBehavior />
</i:Interaction.Behaviors>

to accidentally resolve to Microsoft.Xaml.Behaviors instead, causing the post-upgrade version of the software to be calling Behaviors instead (which of course is not found). Is this a reasonable thing that can happen? I can't think of any other way Behaviors would be introduced. The target framework is 472.