See this article for a full description.
Looks to me as an jQuery Mobile ThemeRoller bug: https://github.com/jquery/web-jquery-mobile-theme-roller
@turiyag - I opened your test page on IE8 and all icons were visible. Closing as cannot reproduce.
fixedToolbars: add iOS6 to iOS workarounds Fixes #5332 - Fixed header…
… jumps around when iOS keyboard disappears