Changing unit sign not working properly

[kendonB]

library(units)
#> udunits system database from /usr/share/xml/udunits
x = set_units(1:5, "m/s", mode = "standard")
# Sign change works but units printed should be -m/s
x = set_units(x, "-m/s")
x
#> Units: [m/s]
#> [1] -1 -2 -3 -4 -5
# This switches the sign back but shouldn't 
x = set_units(x, "-m/s")
x
#> Units: [m/s]
#> [1] 1 2 3 4 5

^{Created on 2020-02-21 by the reprex package (v0.3.0)}

[Enchufa2]

I don't agree in either case. First, you are introducing a minus sign, and this is propagated to the quantity. There is no such a thing as a negative unit. In the second case, it's the same.