Why is this DLL ignored in a VS 2015 Installer Projects Extension setup project?

I have a Setup Project created with VS 2015 Installer Projects Extension that contains a DLL, which I added to the Application Folder in the File System Editor. All properties are default except Register, which equals "vsdraCOM". The DLL is stored on Dropbox. The Setup project is in the same solution as the class library project. The setup project builds into a working MSI.

Frequently, when I re-open the Setup project at a later time, I see a red dot next to the DLL icon. Mousing over the icon produces "Ignored". This isn't specific to any one project, it happens in all of them.

I have not tested whether this issue occurs:

• With multiple DLLs
• With non-COM DLLs
• With another value for the Register property.
• If the setup project is created in a separate solution.

I am able to build the MSI again without any problems, so it doesn't seem to be having a negative effect. Nevertheless, despite extensive searching, I am unable to determine what is causing this and what it might affect.

This is caused by .gitignore containing *.dll. VS is indicating that this file is being ignored.