Menu is getting hidden behind pdf object in Internet Explorer.

Hi,

I am developing a web app, in which I am using object tag to show pdf files. The page is working fine in Chrome, Firefox browser and other browsers too except for Internet Explorer.

Problem:
The submenu options are getting hidden behind the pdf object tag in Internet Explorer(all).

Reference:
1. http://stackoverflow.com/questions/27655374/sub-menu-is-hidden-behind-pdf-type-object-issue-in-internet-explorer?noredirect=1#comment43754776_27655374
2. http://stackoverflow.com/questions/27655470/sub-menu-going-behind-the-pdf-using-html-object-only

I have looked into many blogs and forums but couldn't find the solution.

Please don't suggest the solution which is proposed in the below link,
http://stackoverflow.com/questions/25760079/jquery-combobox-behind-embedded-object-ie-only
as the above link is for select drop down, and my submenu are based on ul li tags.

Guys, is it a known bug which is in IE?
Thanks