Why doesn't "Share on Twitter/Facebook" box appear upon click of Disqus "Like" button when using IE7?

Beneath any article with Disqus embedded, there is a Disqus "Like" button which should produce a box asking "Glad you liked it. Would you like to share?"

See, for example, http://www2.hedgeye.com/newsletter/14299-pax-canadiana.

Our problem is that when using IE7, the aforementioned "Share" box doesn't appear. We use Airbrake (formerly Hoptoad) for bug reporting, but no bug corresponding to this showed up there.

We tried changing the user agent in Safari to IE7 to see whether Disqus is set up to respond to IE7 that way. But when we clicked the "Like" button, the "Share" box did appear.

No script errors are reported by IE7 in the JavaScript console when the button is clicked.

What could the problem be?开发者_运维百科

What else might we test to discover the problem?