With maps that you start only with your knife the player models are like sleeping when using the custom knife.
This happens with maps you start without any weapon/knife too. I saw a post on Alliedmods exposing this glitch after the revolver update but now i can't find it to show you.
Edit: Found it:
https://forums.alliedmods.net/showthread.php?t=276231
Is there a way to fix this?