This is not a bug this is how android works because you have not set a viewport meta tag the android browser zooms to what it thinks is a good level when the page loads and then it zooms to a new "good" level when you change orientation. But zooming a fixed position element actually scale elements in android browser ( creating the whitespace you see ). if you set a viewport meta tag like this to enforce the initial scale
<meta name="viewport" content="width=device-width, initial-scale=1">
you will not see this problem any more ( unless you zoom ) While this is less then ideal its just how android decided to implement fixed positioning.http://jsbin.com/ukUvAVUR/6/edit using that meta tag no longer exhibits this issue.