When changing weapons, you continue running forward even though you don't push any keys, and you're not able to stop until you've changed weapons.
If you try to strafe when changing weapons, it doesn't react and just continue running forward.
Also, sometimes when switching from fx. M4A1 to Fire Axe (other weapons too), your character still stops to change weapons.
If you weapons is lowered, you'll continue to move forward while changing weapons. If your weapons is raised, your character will stop and perform the change.