Why should a lectern be lockable:
We are asked to lock chests & lecterns when we make a map for realms, I am a map maker.

The bug
When you update the nbt data of the lectern with:

You can still open the block as normal without needing an item renamed to lock.

How to reproduce:
1. Place down a lectern
2. Run /data merge block <coords>

at the location of the lectern
The lectern is not locked and I can read what is inside.