I was adding channeling for solid tnt blocks, to make it possible to fuse them with a trident. So the tnt should ignite after been hit by a trident with the channeling enchantment, but that did not work.

I had two tridents: an unenchanted trident and a channeling trident.

The bug always appeared, when pulling a trident as far as it goes and then changing to the other trident. After releasing the pulled trident, the other would be thrown away. In creative mode you actually don't throw the trident, so i was confused with my command at first (but it works), because the commandblock triggered channeling on the unenchanted trident.

The effect vanishes if you scroll to a non-trident slot.

How to reproduce:

1. Place two tridents in your hotbar
2. Pull one trident and switch to the other
3. Release the second trident

As I said, in creative mode it is rather inconspicuous, so you may need an enchantment to see the difference.