When there is an env: matrix at the top level, jobs: include: get one of the env variables (the first?) in the matrix. It seems unhelpful to do this.
e.g. Lint job in https://travis-ci.org/jayvdb/moban/builds/558230993
As you point out, env is a matrix axis which will be expanded to create a set of jobs to which jobs.include will add jobs. These additional jobs must also have env values set, but obviously they cannot have an array value for its env value, since it is obviously a wrong thing to do. (Not having any value might work, but I’m afraid that changing the behavior may break many existing builds at this point.)