You can´t combine infinity with mending. Is that a bug?

In any Version since 1.11.2, you can´t Combine Mending with infinity. Is that a bug or have you programmed so? If it is a bug please fix it, if not then please let me know.

Steps to reproduce:

1. Get an infinity bow.
2. Get a mending bow.
3. Try to Combine them on an anvil. It won´t work.