No change while using CSS <form target="blank">

I want to open another Window when I use <form> to request a query. So I used target="blank" to reach my goal.

However, there was no change when I click the button. I even could not found any error message when I used "firebug" JS consol.

In server end, everything was OK. So I tried to modify CSS to make some progress. I changed target="blank" into target="_blank", it works.