I have a paper submitted to a journal that is currently under review.
My research supervisor now wants to then submit a similar paper to an upcoming conference, by taking an older version of this same paper, and removing some content to fit the conference page limits.
I would understand the conference paper to make sense for a work-in-progress, to have been submitted at an earlier time before a submission to a journal for review, but the work has already been completed.
Would there a possible ethical problem with submitting a purposefully stripped-down version of a work to a conference, after a journal submission had already made?