Ugh. Programmer didn't account for corner case and QA didn't catch it. The algorithm indicates a supercharger stop when the predicted charge first hits 15%, meaning 15.99%. But then the algorithm goes on to calculate what the final destination amount will be, and it computes 15% again (meaning down to 15.00%) with 0 increased charge being added.
Programmer just wasn't very careful and didn't think about rounding and bunch of other things.
Being a programmer myself, this absolutely triggers me!
I wish there was a way to tell Tesla of this BUG, but of course, there isn't.