Well, that's a nice tutorial on how to perform the bug there Shady. Remember: it works with ANY weapon and the bug can be initiated by rolling or backflips.
By the way, the crouchbug has been around for many versions, but MM doesn't want it removed because he found it amusing/funny.
theres also another way to do it
if you set the LAW reload time really low and then shoot it and then do a backflip you will get a crouch float, this is from what I remember
Some settings in the weapon.ini will cause the gun to have animation bugs, causing you to be:
1) Unable to switch weapons unless reloading
2) Go prone and unprone instantly but can't get up unless facing the other direction
3) Rolling and Backflipping would always instantly cause the crouchbug to occur.