walk slowly after dropping the shield

What I expected to happen was...:
I should stop walking slowly after I drop the shield

What actually happened was...:
I still walk slowly

Steps to Reproduce:
1. walk and use a shield
2. drop the shield and keep pressing right button(the "use item"key in key binds) and w(the "walk forward" key)
3. I still walk slowly but there is nothing in my mainhand