Question: Why do you suppose that some people find a compound called PROP to have a bitter taste, whereas o…

Why do you suppose that some people find a compound called PROP
to have a bitter taste, whereas others do not report this
perception? According to what I know, perception that food is
bitter is dependent on the interaction of the compound PROP with a
GPCR, G-Protein-Coupled Receptor, at the end of the receptor cell.
How exactly does that make what usually tastes sweet to be
bitter?