Znalazlem jeszcze ponizsze:
'Less frequently, the progressive combines with habitual meaning to suggest that every event in a sequence of events has duration/incompletion:
Whenever I see her, she's working in the garden.
[...]
To have this interpretation, the clause
mustcontain an adverbial of time position or frequency.'
Quirk at el, p.198 [4.26]
There's no such an adverbial in this sentence:
Do you listen to music when you're studying?