QSignalMapper::removeMappings does not seems to work

If a widget is mapped with String1 and again if same widget is being tried to re mapped with other QString2 after calling removeMappings(), then Signal is emitted twice with the second parameter String2 indicating first mapping still alive in table and only first parameter QString1 got removed/overwritten.

Attached example reproduces this:
Steps:
Please run the program in the following order:
Start and press button map2.
Hit the button with the "1"
Hit the button with the "2"
Press button map4
Hit the button with the "A"
Hit the button with the "B"
Hit the button with the "C"
Hit the button with the "D"
Press button map2
Hit the button with the "1"
Hit the button with the "2"

Experience output as attached.