Data and reproducibility
It is normal to present the results of the author's research in the conference proceedings regardless of whether the paper was presented, accepted or published. Indeed, this is common practice in many fields. In general, copyright law applies to the original expression of ideas, it may restrict an author from distributing a paper in a conference proceedings, it does not prohibit an author from creating a new presentation using ideas from this manuscript. The journal would do well to explain what the authors mean by the notion of "full text".
It would be prudent if authors did not share an unpublished manuscript with the conference committee to prevent erroneous duplicate publication. Authors should also consider what materials, figures, tables, etc. they would be happy to share before publication and in what format.
It would also be good practice for authors to indicate in the paper that the results were presented in part (or in full) in conference proceedings.