Haha yeah, Heres some steps to replicate the issue.
Do a long jump by pressing space. The press Left Shift and W. The result sometimes ends up with the player dashing to either the left or right and not up.
Maybe its a skill issue on my part, but I find it intuitive to press W and either A or D for the direction. I guess how you could fix this small issue is by checking the up/down directional inputs first and going for those. Or just checking if any up/down inputs are given in a span of 2 frames or so. (to short of debounce the inputs)