Some items such as bows, crossbows, and tridents do not render in the hands of villagers.

What I expected to happen was...:

These items render normally.

What actually happened was...:

These items do not render.

Steps to Reproduce:

1. Create a world and set the game mode to creative.

2. Build a house with a bed and a fletching table in it.

3. Use a villager spawn egg or type:

/summon villager

in the chat to spawn a villager. 

4. Wait for the villager to become a fletcher.

5. Make multiple trades with the villager until level 2 is unlocked.

6. Hold emeralds in front of the villager, he has a chance to hold a bow.

-> The bow in his hand does not render.

7. Make multiple trades with the villager until level 3 is unlocked.

8. Hold emeralds in front of the villager, he has a chance to hold a crossbow.

-> The crossbow in his hand does not render.

This also happens when villagers are given bows, crossbows or tridents via commands.

Type the following three commands in the chat:

/replaceitem entity @e[type=villager] slot.weapon.mainhand 0 bow
/replaceitem entity @e[type=villager] slot.weapon.mainhand 0 crossbow
/replaceitem entity @e[type=villager] slot.weapon.mainhand 0 trident

You will notice that none of them are rendered in the hands of villagers.

This also happens to wandering traders.

Type the following three commands in the chat:

/replaceitem entity @e[type=wandering_trader] slot.weapon.mainhand 0 bow
/replaceitem entity @e[type=wandering_trader] slot.weapon.mainhand 0 crossbow
/replaceitem entity @e[type=wandering_trader] slot.weapon.mainhand 0 trident

The result was the same as that of the villagers.

This bug doesn't exist if you give them items that aren't bows, crossbows, or tridents. For example:

/replaceitem entity @e[type=villager] slot.weapon.mainhand 0 stone