So far as I know, my musical borrowings have all been conscious, or if unconscious I detected myself them during the writing process.
Jerome Kern and George Harrison were found guilty of unconscious copyright infringement. In Kern's case, at least, I think the court goofed.
According to The Times (London), Richard Stilgoe (lyric writer for musical plays) advised people who wanted to avoid unconscious copying to "get their music vetted before release. 'I might write something I think is wonderful, then I play it to my family and they say "yes that is wonderful, but it's Land of Hope and Glory."'" Caroline Lees, "Does this tune seem familiar ?", The Sunday Times (London), August 2, 1992.
This is one of the reasons why musicians need a rich public domain to draw on. Creative copying, whether conscious or unconscious, is a part of the process of making music, and sometimes some of this creative copying would be actionable under copyright law. If we weaken copyright too much, writers have trouble making a living. But if we strengthen it too much, creativity bogs down in monopolistic stagnation.
The present situation in the U.S. is one of overprotection. The term of copyright should be cut in half, the music licensing system needs reform, the boundaries of fair use may need some adjustment, and the anti-circumvention provisions of the DMCA need to be repealed.
For a discussion of possible musical borrowing by Lewis Beethoven, click here
For the Indiana University bibliography of musical borrowing, click here.