I finally figured this out. Setting tools/options/html_designer/css_positioning to "no positioning attribute" eliminates some of the problem, and should be done. The remainder of the problem is caused by accidentally dragging controls on the form. The mouse pointer does not behave properly in Visual Web Developer. When I try to drag the window scroll bar, I try to pay attention and make sure it's an arrow, but more than half the time the pointer is a resize or move shape. Even though the mouse is over the window scroll bar, it retains resize/move functionality from the last control it passed over. Because I have page margins set to zero, and because view controls span the entire width, the IDE carries resize/move over onto the scroll bar. When I want to scroll I must move the mouse around, watching the pointer twitch and assume different shapes, and only when it's an arrow, attempt clicking on the scroll bar. This is a severe pain and nuisance. Obviously I have seen that the window will not scroll unless the pointer has the correct shape. What I did not know was when I clicked and attempted to scroll with the wrong shape, I was doing a resize/move function. Because controls remain aligned to the grid they don't actually change, but the action is enough to make the IDE place width or height attributes on the control.
I guess I just have to pay more attention, as if things aren't tedious enough. If enough people mention they are having this problem, maybe Microsoft will address the issue in a future version. Resize/move functionality for controls should go away if in proximity of the window scroll bar, or a "lock controls" checkbox should exist for the page similar to what we had with VB6.