CSS styles provided with ext- are not working on IE8 with HTTPS(SSL).

Throws the security warning as css classes contains about:blank urls as background-image. one e.g. below

body.x-nbr .x-btn-default-small {
/* Pass along Div/Table, Horz/Vert, border-radius and border-width: */
background-image: url("about:blank#th-3-3-3-3-1-1-1-1-2-2-2-2");

Also buttons and tabs etc. are not getting styled.
Issue only on IE8 with HTTPS (SSL). With HTTP it works fine.