My guess (and its a guess) is that you don't have axis direction the same as linuxcnc thinks it is.
Everything hinges on the direction being the way linuxcnc assumes.
The screens show tool direction and depending on your machine it can be opposite of what you expect.
note in this diagram the top right shows tool movement but the movement shown on the machine's table is opposite.
linuxcnc.org/docs/2.8/html/user/user-con...chine-Configurations
Here is a homing example diagram (this is from 2.8 docs, but the diagram is the same in 2.7):
linuxcnc.org/docs/2.8/html/config/ini-ho...witch_example_layout
So you must start with the _tool_ moving in the positive direction when you press the positive jog key, even if it's not the tool moving.
It's kinds hard to explain and that might not be your problem but it seems to lead me there.