Ok so there it is. When you do a flip (the basic one, where you hold only one direction key (a/d)) do not release W, but instead hold it and press/hold right mouse button.
If you do it properly it will make the gostek stuck in a crouch position, and you will gain awkward horizontal speed, witch you can change and adjust by pressing/releasing RMB and moving mouse from right to left.
If you still can't get it (it works 100% of the time if done right):
Add RMB (still hold W)
>flip animation< (still hold W)
Notice bugged animation
Move your mouse around pressing, holding RMB
Same goes for fliping right ofc.