The Bug:

You can place lily pads and frogspawn outside of the world border and inside spawn protection.

Please note that the issue isn't a desync.

Steps to Reproduce:

1. Summon a large area of water below your feet by using the command provided below,

   /fill ~10 ~-1 ~10 ~-10 ~-1 ~-10 minecraft:water

2. Set the world border's center to your current position and to seven blocks wide by using the commands provided below.

   /worldborder center ~ ~

   /worldborder set 7

3. Switch into survival mode, obtain some lily pads and frogspawn, and attempt to place them outside of the world border.
4. Take note as to whether or not you can place lily pads and frogspawn outside of the world border and inside spawn protection.

Observed Behavior:

Lily pads and frogspawn can be placed.

Expected Behavior:

Lily pads and frogspawn would not be able to be placed.