It's like the release_key_event get lost sometimes, so when i move with the WASD keys sometimes one of the movement keps going on also after i released the associated key.
This is the second time it happens during the last 2 weeks, i never had this problem before.
The first time was while using the unstable client 4.00 when i was riding my cart and turning right with the key D as soon as i released the D key the cart kept turning right, after a few seconds trying to understand what was happening i hit the D key again and when i released it for the second time finally i stopped turning right.
Since that eposide i went back to the stable client 3.99z but this morning happened again while i was walking forward with the key W, as soon as i released the W key i kept walking forward and i had to press & release the W key again to stop it.