I can't place trapdoors on farmland.

I used to be able to, but now I can't and it's frustrating because of the requirements of my new building project.

All you need to do is have a trapdoor in your hand then tap on the farmland as if to place it. It won't place!

If this is intended, then it's fine and I understand, but it's quite frustrating.

Wheat with trapdoors around it looks very nice...