Rewrite module to handle site version folders (strip slash)
It looks like this is interfering with mod_dir, which by default redirects the browser when it tried to access a directory and the trailing slash is missing. What's happening is the Rewrite is occuring, changing /site to /versions/020/site then mod_dir is redirecting the browser to http://domain.com/versions/020/site/. Thus the browser sees the versions/020 stuff in the location bar.
You can turn off mod_dir's automatic redirect with the "DirectorySlash Off" directive. But you may want to add the trailing slash anyways by including a redirect before any rewrites happen.
RewriteCond %{REQUEST_FILENAME} -dRewriteRule ^(.+[^/])$ $1/ [R,L]This or something equivalent before you do the rewrite to /version/020 should hopefully fix it.
Edit: Actually, now that I'm thinking about it, if you rewrite/redirect when trailing slash is missing, you don't need to turn off DirectorySlash because it'll always have a trailing slash by the time it gets to mod_dir. Maybe do it anyways to be safe?