Why is my web page expired after Spring WebFlow redirects?

Question

I'm using Spring WebFlow 2. Here's my situation.

View states: state1, state2

Transitions: state1 goes to state2 if validation passes

state2 pops up a new window using the following:

<view-state id="state2" view="externalRedirect:${flowScope.myUrl}" redirect="true" />

I want to be able to continue my business at state1 after the window pops up. Normal flows don't seem to have a problem.

But here's when things go bad.

1. I'm in state1. There's a form to fill out.
2. I fill in the form but it doesn't pass validation.
3. I fill in the form again.
4. I get to state2 which just pops up a new window with the URL set in the source code.
5. The existing window goes back to the form.
6. I fill out the form again, submit.
7. IE says web page has expired.

Can anyone tell me what's going on please? Is this the right way to pop up windows? Thanks.