Prevents a 1.14 glitch that allows players to hold a Silk Touch book in hand, and break a block. This will cause the block to drop as if a silk touch TOOL was used on the block, meaning items like glass, ice etc can be quickly mined without having a properly enchanted tool.

http://prntscr.com/obf8de

The new protection will prevent the block from being broken and send a message to the log/staff.