The xmlhttp in IE ModelessDialog problem

Make a button and use window.showModelessDialog to create a ModelessDialog .in this Dialog , call xmlhttp code to access xml data.
Click the button,Before the data has loaded,close the ModelessDialog,and click the button ,open the Dialog,and close the ModelessDialog before the data loaded.After twice like this,you can find that the button onclick,no answer,if you close the ModelessDialog after the data loaded every times,everything in gear.

using xmlhttp.abort before the ModelessDialog close can avoid the problem,but how can i do ,if the grid created in ModelessDialog ,like "The xmlhttp in IE ModelessDialog problem".