It doesn't matter whether gnome-screenshot is invoked with the -w option, with or without the -b or -B option, it takes the entire screen.  It appears to also ignore the "Grab the current window" button in interactive mode.

To reproduce:

1.Invoke gnome-screenshot with the -w option, with or without the -b or -B option.  Alternatively, use the -i option and choose "Grab the current window".
2.Save the screenshot to a file with an appropriate name.
3.Observe that the file is the size of the entire screen and contains an image of the entire screen.

Attachments showing screenshots taken with various options are available in the Mandriva bug report at https://qa.mandriva.com/show_bug.cgi?id=56652