IE blocks NavigateToURL as pop-up. Workarounds?

[Handycam]

On a game we just completed in Flash Builder 4, there are a couple of links like this:

var sponsorLink:String = "http://www.plantersplace.com/";
navigateToURL(new URLRequest(sponsorLink), "_blank");     

IE 7 in some installations is treating this as a popup. Firefox 3.6, Chrome 5, Safari 4 all fine.

The game in question is at http://game.finegardening.com/

Click "continue without logging in, then click "show hint".  Click the hint.  This should fire the above code and open a new window.

Several users in IE report this gives them a pop up alert.  I am trying to find out why and what can be done about it.  I have tried the solution I found at Zorked but people STILL say they are getting popup alerts.

[kglad]

you're coding it as a popup so if users have stringent enough settings, they would be expected to be warned.