Tested on versions: 1.14.4, 1.15.1 

Steps to reproduce:

1) Place a lectern

2) Put any book on it

3) Try to replace it with air(or other blocks) using commands(/setblock, /fill or /clone)

Commands working fine when in singleplayer or Vanilla server. 

This bug is not so critical, but I need a fix so I can create a custom map with my friend(we need spigot only for WorldEdit and better performance).