Paypal Hangs

I have an application that uses the PayPal integration. For most customers it works perfectly. However some after completing the PayPal function they get please wait screen do not close this screen. The transaction is completed but the please wait screen never goes away. I have not been able to find a pattern. I know it has happened with Internet Explorer 8 and Safari and possibly other browsers.

Have other people seen similar results?

Herb Wexler