Selecting a square box using marque tool with shift held down bugs out and occasionally 'jumps' in size while dragging. Generally one of the sides is 1px off, if you drag from top right or bottom left, diagonally. When dragging from bottom left it jumps to incorrect size when it reaches 11px in gif below.
Expecting same sides in pixels, no matter how selection is made, with no "jumps".
PS. Issue doesn't appear when creating a vector rectangle, just marquee.
Ive reported this once, in beta (1.5 or 1.6).