Link To Page Using Target Blank & Linking Page's Window Location?

Basically, I have a link that should open the targeted link in a blank page, and upon the link being clicked, the original page's URL should be changed. The reason for this is that the user has to browse information on another website, and then pass the information on to me via a contact form, so rather than make them click back on my tab in the browser, and then find the "Contact" page link to fill in the form, I thought it would a good feature to simply go ahead and load the "Contact" page upon them clicking the link to the external page (which of course loads in a new tab). Here is the code I have in place:

Code JavaScript:
<a href="http://www.othersite.com/" target="_blank" onclick="window.location.href='http://www.mysite.com/contactus.php';">Other Site</a>

This all works fine on my computer, regardless of the browser that I use. One of my partners on this project called me this morning and said that the link was taking him directly to the "Contact" page without opening the "Other Site." This is strange because after I put this in place, I showed it to him and it worked fine. Now, a few days later, and it does not work. He said that he cleared his browser cache, history, cookies, etc. and the problem did not go away. He uses IE8. After he told me it was no longer working, I went to test it myself, and it works fine for me no matter which browser I use (IE8 or 9, Firefox 3 or 4 Beta).

why this might have worked one day and not the next? Is it simply a problem on his computer, or could it be an issue where based on what type of browser you are using, this won't work. Also, I know this is the JavaScript forum, but is there a way to do this in PHP without using the JavaScript onclick event? Obviously, I can't use the header() function since this functionality needs to be present on a link within text of a page.