While sitting in a minecart, stopped on a sloped, non-powered powered rail, if you push forward (W) facing up the slope to manually move the minecart up the slope, it will instead roll down the slope.
Linked issues
Comments 7
Affects 1.16.3
Affects 20w45a
Affects 1.17 Pre-release 1
Affects 1.17
Affects 21w40a
Considering the first affected version of this report is 1.14 Pre-Release 4, I would say this is likely caused by MC-169854 (minecarts move slower in versions past 1.13 when using the W key).
If it is not close enough to be considered a duplicate, I can confirm in 1.21.
Affects 1.16.1