When you sleep in a bed that is on the same height as your head (standing one block beneath it), everything is normal, but if you sleep standing on the same height as the bed, on the bed or jumping while entering the bed, the camera glitches into the player model. But that also seems to be affected at which angle you click the bed at which height.

The screenshots are taken while sleeping after use-clicking the bed:

• From standing one block lower than what height the bed is placed on
• From standing on the same height as the bed is placed on
• From standing on the bed
• From jumping higher than the bed

To recreate just place a bed, set the time to night, have a height difference of one block up from the foot of the bed. Use-click the bed. --> The camera glitches into the player model.