[GAMEPLAY] Tempered fate (Bard Ult) and approach velocity not working?

Is tempered fate not supposed to work with approach velocity?

PASSIVE: Gain 15% bonus Movement speed when moving toward an movement impaired allied champion, or toward an enemy champion whose movement you have impaired.

And stasis is listed as valid crowd control for impaired movement in the wiki.

But you can see from the gif it seems tempered fate only procs approach velocity for a split second (330ms to 380ms). Whereas with regular cc (cosmic binding and meeps) the rune can be seen working with increased movespeed for the duration of the cc. Is this intended or am I missing something?