AJAX :: UpdatePanel Is Not Compatible With CreateUserWizard?

I have a updatePanel inside a createUserWizard. Such arrangement is to let guest to test if their selected username is available to use. However, when user clicked the button to check its username availability, everything works fine; the inputed name will be examined and the availability will be returned from such partial postback. What strange is, when I clicked the "Create User" button, the page was posted back to server but "CrWizard_CreatedUser" doesn't fire. Then the page was sent back to my browser and i have to re-enter the password and press the "Create User" button and this time Crwizard_CreatedUser is fired.

I re-test this situation again by not pressing the "Check Availability" button and hit the "Create User" button directly after filling out the form and this time, Crwizard_CreatedUser is fired. I doubt if something has changed secretly after I hit the "Create User" button. Hope someone can tell me what goes wrong.

<asp:CreateUserWizard ID="CrWizard" runat="server" OnCreatingUser="CrWizard_CreatingUser"