Just disable alphablending and antialiasing. Or create a new layer, it not actually a big effort.
(Thanks for the shortcut, Rick, I promise you I will read the Help some day
Image > Flatten.
It's not bugged, Undo shortcut is Ctrl + Z. Delete key delete the selection.
Private joke.
PdN allow you to do step by step selections.(http://www.eecs.wsu.edu/paint.net/doc/2.6/Help/en/SelectionTools.html) This will be annoying for people you want to use this trick.
Tablet-PCs focused reasons (just a pen, not always another button)
Did this mean we can expect it for a near future?
Anyways, interesting discussion!