Disclaimer: I do not know if this is a bug or not.

Hostile mobs can and will attack players while they sleep. When they are attacked, they exit bed, as if they left bed on purpose.

What I expected to happen...:
Players in bed are unaffected by hostile mobs.

*What happened...:"
A player was targeted and attacked in bed. After being attacked, the player left the bed.

Steps to Replicate:

1. Sleep in a bed with a mob somewhat near you (or you can just have some specific mobs next to you, see MC-92719)
2. Wait to be woken up by being attacked.
   Note: It helps if the world is multiplayer (the only mode I could test it in), so that you do not fall asleep immediately.

Once again, I do not know if this is a bug or not. Thank you for your time.