If your selection is smaller than 14px in either direction, you cannot move the selected pixels. Instead you can only resize the pixels.
This seems to be caused by the resize zone extending 7px from the top and left of the selection and 6px from the bottom and right of the selection. When the selection is smaller than 14px in either direction, the 1 moveable pixel zone in the middle disappears and you can't move the selection.
The resize zone should instead behave more like mspaint (*gasp*), where you have to be on the border to resize the selected pixels.
