A THREAD FOR NEWCOMERS!

Either a bug or an artifact of the "Sphere of Suppression" (or whatever this sphere is called).

This sphere is called the Sphere of Vulnerability (or Medal, although its appearance is that of a sphere).
For more details on how this Sphere works, see Physical Magic, section 5.4: Sphere of Vulnerability. Features of its use in battle. There are a number of not-so-obvious nuances that determine its effect.

And the Sphere of Suppression prevents the use of magic in battle - without any exceptions.