Illustrator can not adjust rounded corners of shapes when draging cursor on the adjustment dot

When I put my mouse cursor on the adjustment dot located in the shapes' corners, my cursor correctly turn into the style of adjusting rounded corners, but when I hold and drag my mouse, the shapes just won't turn into rounded corner ones but will only rotate as I move my mouse.

However, such things only happen only when I'm using the "Selecting Tool (shortcut V)", not when I'm using the "Direct Selecting Tool (shortcut A)".