Mojang priority is greyed out

I try to change the Mojang priority, but it’s greyed out. This is a bug!

What I expected to happen was...:
To be able to change the Mojang priority.

What actually happened was...:
Instead, it’s greyed out.

Steps to Reproduce:

1. Open the bug tracker
2. Create a bug
3. Try to change the Mojang priority
4. Notice it’s greyed out

Workaround

1. Click Configure Fields
2. Uncheck Mojang priority
3. Recheck Mojang priority
4. You can now change the Mojang priority