I always thought this property has something to do with suppressing reporting engine updating display/status bar or something like that.
Turns out this property can actually suppress fully blown errors.

With listener property 'QuietMode' set to .T. ,
You can have something like;

*method render
Wait Wind cNonExistingVariable

And report/code will still run ?!??
Made debugging my listener to be very nerve racking venue until I discovered this... uhm .... Feature ! {g}