Blanket.js coverage doesn't work with functional change file

Basically as described above. Blanket.js coverage doesn't work with functional change but works with regular change. Is this something that can be fixed or does it just not work with the functional version?

Start by reproducing the coverage failure with Blanket.js for the functional change and compare it with the regular change, using the repository's existing tutorial examples and tests as entry points. Determine whether coverage can work for the functional version; done means the failure is fixed and coverage behaves consistently, or the limitation is documented if it cannot be fixed.

Written by the indexing model from the issue text.