The z-index works improperly when setting it on a popup. The causing reason is when popup does float, it would set its z-index to become the top at the desktop, even though the user set the z-index manually.
For example,
1. user set <window id="win1" visible="false" zindex="200"/>
2. click button <button onClick="win1.deOverlapped()">
After click the button, the z-index of the popup window is 1800 rather than 200.(it should be 200).