javascript "switch" statement can not go into correct case block with MinGW 32bit in release

The switch statement in javascript sometimes doesn't work correctly in my application built with Qt 5.1 RC.

switch(A) {
case B:
...
}

when A is a string variable from DOM and B is a string literal longer then 3 characters, the code in B block can never be executed even if A===B.

the attachment test.html shows this bug.

click button "Test1", the message is always "your selection is **** !?" in default clause which shouldn't be executed.
click button "Test1.1" or "Test2", the message is "*** selected"