Refocusing on a different window without losing form data?

[MartyNg]

I've never stumbled into this before. From Window A, I am using
window.open to open Window B. Window B has a form with lots of
elements. If the user loses focus of Window B somehow, and they click
the link on Window A to open Window B, all the form data is lost on the
refocus. I could have sworn I had this working before with the same
code. Do I have to conditionally check to see if Window B is already
open? (That way, I could just focus on Window B instead of reopening.

<a href="javascript:void(0);" onClick="var testWin =
window.open('testFormPage.asp?numItems=10','LocationWin','');
testWin.focus();">Open test form in new window</a>