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
relates to 2
Comments 7
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