Since version 1.13 you can no longer use the item in your offhand if the block in your mainhand cannot be placed, which is intended per MC-126337. However, this doesn’t apply to lily pads. If you cannot place the lily pad because of an entity standing in the way or the targeted block not being applicable for placing lily pads, you will still be able to use the item in your offhand.

Steps to Reproduce:

1. Hold a lily pad in your main hand
2. Hold a snowball in your off-hand
3. Try and place the lily pad on a block which is not normally applicable for placement

Expected & Observed Results:

- The snowball will be thrown.
- The player would not throw the snowball item, as they are currently attempting to use the main hand to place a block/item.

Screenshots/Videos:

MC-218114.mp4

Notes:

Related to these issues
MC-256407 MC-136405 MC-237476 MC-226518