"Fasten seat belt while seated"

I have no problem understanding what is meant by the above exhortation. I am just curious as to whether native speakers find it odd or perhaps even incorrect. The obvious idea is that passengers are advised to keep their seat belts buckled up whenever they sit in their seats.

However, my dictionaries don't credit fasten as a transitive verb with such a meaning. Supposedly fasten only has meanings that denote the act of fastening something, not the state.To my ear, which has been tarnished by studying too many foreign languages and the ever-present influence of my native language, the sentence seems to imply that passengers are requested to spend the entire duration of being seated in the process of fastening their seat belts. Fastening the belt can thus take hours!

I don't mind if anyone disagrees with me, but to me this is just another trivial example of the inexactness of English. I wonder if anybody agrees with me?

Cheers, CB