classical I've composed a brief sketch of a mazurka.

Wow what a great example of plagarism that is. If you really want to use other composers' theme, you should announce them right at the beginning in the title. Like Brahms' variations on a theme by Haydn, Paganini, Schumann etc., but not saying that you compose the theme by "drawing inspirations from Chopin". That's not drawing inspirations, that's plagarism. I myself think that using other composers' theme is OK if that really fits the context of your composition and you announce the use of it. There will indeed be some usage in the subconscious level. But not like this, this is obviously copy in a conscious level.

What Stravinsky said was to treat past music as material which you have to creatively transform it to something unique. Ravel transformed Mussorgsky's Pictures at an Exhibition beautifully with his own colour, that's why he should claim the credit of an orchestrator. And he didn't claim he drew inspirations from Mussorgsky and wrote the music by himself too.