The bug
A bed can be placed directly next to the worldborder causing the head part to be placed outside of it. Expected would be that you can not place a bed that way.
How to reproduce
Face the worldborder and place a bed directly in front of it
Related issues
relates to
Attachments
Comments

Can confirm for MC 1.12.1.
Confirmed for 1.13.1-pre1
Confirmed for 1.13.1
Can confirm in 20w48a.
Can confirm in 20w51a.
Can confirm in 21w03a.
Can confirm in 21w06a.
Can confirm in 1.16.5 and 21w08b.
Video attached.
Can confirm in 21w15a.
Can confirm in 1.17.1.