I don't understand. What do you expect the dimension box to do with the arrow key input? If I single click in the dimension window, then the left and right arrow keys shift me left and right in the dimension, as I would expect.
Yesterday, impossible to make the left/right arrows keys working, in the dimension box.
This was in a 3D sketch, in an asm.
To edit the datas, i used the left panel Dimension, the field Primary value, but with the popup box, impossible to make the keys working.
Today, all works good. Very strange.
I found where is this bug.
A 3D sketch, in a asm (perhaps this behaviour is in others occurences).
1- you click on an existing dimension.
Then, the left panel "Dimension" is opened
2- you dbl click on the dimension, then, the popping up box is popping up, but then left/right keys don't work in this box.
I hope that this post will help.