Charge rank 3, can't train it?

[smoothoperator]

I tamed Bellygrub to get Charge rank 3, so far so good. The point was to teach it to my main pet, another boar. But even after taming Bellygrub, the skill is not available in the Beast Training page.

Is this a bug or am I missing something here?

[Overtime]

Keep using the skill until it says "You have learned charge..."