The rectangular region mode can fail to respond to keyboard inputs and double-clicking, attempting to escape out of the mode can also be pretty much impossible as it insists on displaying above everything, this is a very bad design flaw!
The region mode should allow the user to crop the screenshot that was just taken without taking full control of the screen.
*** This bug has been marked as a duplicate of bug 374009 ***
Changing duplicate to a more fitting bug.
*** This bug has been marked as a duplicate of bug 386629 ***