Duplicant performs construction supply with both supply and build disabled.

Was the construction paired with a dig job? Is your dupe allowed to dig?

There was no digging involved.  I discovered that what was happening is the duplicant was doing a sweep job and she supplied the materials as a consequence of that.  There was some sandstone marked for sweeping and she didn't have tidy disabled.  I am not sure this is a bug so much as it is drawback in the job system that prevents it from being useful.  I have duplicants that I want to sweep and in doing so they end up contaminated with germs so I do not want them to supply materials because it will spread germs.  To facilitate that I disabled every type of skill that says that it does supply for the duplicant that is associated with the tidy job, but I still can't stop her from delivering supplies.  There should be a way to separate supply jobs which spread germs from sweep and disinfect duties which attempt to quarantine or eliminate germs, but there is not because tidy (sweep) overlaps with too many other skills.  If you allow a duplicant to tidy then your settings for storage, supply, cook, build, life support, research, operate, and farm are all useless unless you don't ever use sweep.  Sweep should either only have storage as a destination or it should also consider whether storage or supply are enabled to decide whether to allow sweeping for supply purposes or sweeping for storage purposes.