selected text becomes unreadable

I'm using Visio 2003 SP2 on Windows XP. Recently there was a change that
caused selected text to be rendered as a blue box so that none of the text is
readable.
If I use the text tool to select a text object, the text is replaced with a
blue box as wide and as high as the text. The text is black on a white
background (the default).
If I move another window (such as the window in which I'm composing this
message) over the Visio text, the text is rendered in white on the blue
background.
It doesn't seem to make any difference whether the text is 5pt or 12pt. I
get the same behavior either way.