The double stuff might be caused bu the modal callbacks subsystem, If you want just a simple window that displays a messages and has a OK/Cancel button this will work
ret = utils.questionWindow("title", "message", "OK", "Cancel")
if ret then console ("true") else console("false") end
Of if you want to get a text response from the user, you can use the other method in the utils
askForTextInputWindow (const String title, const String message, const String initialInputContent, const String onScreenLabel, const bool isPassword, const String button1Text, const String button2Text);