Incremental builds for .vcxproj build customizations broken in recent updates?

I am seeing an issue in recent updates of VS 2017 where incremental builds do not work for files that are built with a build customization. This has worked with my build customization for every version of VS including the original release of VS 2017, but no longer works in recent updates (eg, update 8).

This can be reproduced with the Microsoft MASM build customization (I have a project that reproduces this but I do not see a way to attach .zip files to posts):

1. Create a new VC++ project.
2. Add the MASM build customization to the project.
3. Add a .asm file, build project.
4. Edit the .asm file, build project again.
5. Result: It says the project is up-to-date, it does not rebuild.

Is this a bug in VS or does a change need to be made to support incremental builds now?