It's intentional, at least as far as Dualcast's description states. The term "ability" in a tooltip always refers specifically to skills that have that classification as opposed to something like "spell" or "weaponskill." Sprint doesn't have the classification "Ability" so it cancels the effect. It doesn't have any classification at all, actually, so whether Sprint
should have a classification might be up for debate.
The Dualcast tooltip:
https://i.imgur.com/SN5K68R.png
The Sprint tooltip:
https://i.imgur.com/FJhSPyI.png
The tooltip of an action showing the classification as an Ability so it doesn't cancel the effect:
https://i.imgur.com/PHPCkVT.png