It probably considers anything in the lower 180 degree range as "down". My builder character is in solar armour and it's always dashing when I don't want it to, and that's always after a stutter. I just watched your video and you're definitely in vortex stealth.
I also watched your cursor video and I have the same issue. I found that when I unequipped all range extending items (architect gizmo, toolbox & tool-belt) that it stopped happening. I then measured the length of the "snap back" and the cursor always ended up to the default reach, by which I mean with no range extending items. It's like the game keeps on forgetting - for a nano-second - that you are wearing them.