In printable versions of articles, they lack the noindex meta tags and sometimes google, which will only
index one version of a page, will index the &printable=yes instead of the regular. Note that Wikipedia's
solution of telling robots.txt to index anything at all with "index.php" in them is not feasable for
most wikis. There are settings in the includes folder for different meta tags in different aspects of
viewing (like viewing history, previous versions, special pages, etc. that sometimes vary) so there
needs one for printable versions, which should default to have a meta noindex tag -- I am not sure where
in the many files this would be to modify it myself as a text search on all files for "printable"
doesn't turn up the right one.
Right now I've done a sort of fix by removing a line from Monobook.php so the printable versions
redirect to the standard.