Are you sure you're not spamming the left shift key to get running again, that brings up a sticky key prompt on my system.
The default action for bringing up the sticky key prompt is in fact 5 consecutive presses on the shift key, it does exactly that on my system as well, so 5 presses with no other action will activate that popup, however it has never, and I do mean never, popped up while I am in game, so there must be some odd setting in the OP's keybinds or keyboard settings that is causing it. Since we don't have access to those we are essentially guessing.
As can be clearly seen in the image in post #13 - the box to enable that is unticked.
Can we please forget about the sticky keys warning* - it is a diversion from the actual suggestion - to enable a toggle option in the move forward control binding.
Thanks
* It is not as if it happens all the time, just randomly every so often - I really REALLY REALLY wish I had not mentioned it at all.