Navision is the truly crappy system that for some reason we use at work. It sucks for many, many profound and fundamental reasons, far too numerous to go through.
Simple in terms of basic usability design the program sucks harder than an asian hocker. With inconsistent mouse support, lists that lock up when scrolling, lack of keyboard commands for simple functions and so on.
But my favorite is the ‘esc’ key. The escape key. Depending on where you are in the interface this key can either mean ‘oh shit, i didn’t want to do that’ or ‘yes please, that is right, keep my changes’. With logic like this I’m surprised that the delete key doesn’t sometime insert stuff!!!