DPI scaling limits window size

I am using Windows Vista Home Premium on a PC with a 1920x1200 pixel
display.

I increased the Font Scaling to 144dpi and get good usable results,
but if I do not check Use Windows XP style DPI scaling, maximised
windows are just 1260 physical pixels wide, and the right edge of non-
maximised windows seems to be limited to a 1260 pixel boundary. Mouse
clicks beyond this boundary to not seem to be recognised (eg right-
clicking to change display properties) even though the mouse pointer
can be moved beyond it.

If I check Use Windows XP style DPI scaling, windows and the mouse are
able to use the full screen width.

Is there a fix available for this bug?