The character goes prone then up when vaulting while moving forward while in any other stance other than default. (eg. crouching, tall, low crouch.)
Vaulting works normally if player is standing still.
eg. Tall stance > "V" > normal stance > vault
If player is moving forward and vaults, Character goes prone first before getting up to vault.
eg. Tall stance > Moving Forward "W" > "V" > prone > normal stance > vault.