Resolving fields fails in self-join because of missing columns

Hi Chris,

Following the fix from 9bdc898054dcac0c98b42d1d3c0fbaed46492a9c, I am now encountering a new issue where it seems that the projected value columns are dropped during planning. See attached a unit test reproducing the problem.
I have not attached an expected result file (see todo in unit test), as I am not sure what would be the correct output for this query.