dimension lines: why does changing the text size change line lengt

I recently moved to Visio 2003 and have been using the new stencils in it. I
added some "controller dimensions" from the office layout group (walls, doors
and windows, US) to a drawing. They are not "connected" to anything because
they are measuring parts of complex and grouped shapes.

I changed the size of the font on the dimension lines and found that the
length of the lines would change. I've never seen a dimension line do that in
any earlier version.

What on earth is going on? How do I make that behavior stop?