mtb:scale:uphill=-3
was used here, see https://www.openstreetmap.org/way/1029868654/history

Maybe
mtb:scale:uphill=3-
was intended here?

I am pretty sure that it is a typo, but not sure enough to just replace it (I edited some objects where situation seemed more clear to me).

Or maybe this value was used deliberately? In such case, what was the intended meaning?

If you know it is a mistake - can you fix it?