Vorpal swords and derivation

'And his vorpal sword went snicker-snack...' - we all know where it comes from and the derivation automatically carries us to a certain mental setting for any story it is used in. Sort of instant setting-gel. Now this is a valuable tool (shared associations) for writers - but it is also a very dangerous beast because it is so infectious. Books - particularly when the author has a distinctive style and voice creep in to my own writing like memes-in-the-night. I try to work with this if possible - When I was writing the Karres books I read only Schmitz to try and be influenced by it (and in the last one I slipped and read an Andre Norton - I can SEE the influence). I use combinations of other writers to 'set' myself for other kinds of books. CS Lewis, Michael Scott Rohan, Peter Beagle, and McKillip, and a dash of Heyer for Dragon's Ring for eg. Or for Slow Train to Arcturus, Heinlein, Niven, Hal Clement. For Rats Bats and Vats - Tom Sharpe, Terry Pratchett, Niven.

So: am I alone in this, or do others find themselves writing derivative style and voice? And if so, how do you control it and who do you use?
I have fairly limited access BTW, so commenting is difficult for me right now.