>>Perhaps another thing to check is what fonts were being specified at design time -- I do vaguely recall in the case where the specified font is not available, Windows may select the "closest match" -- which may or may not all that close in appearance.
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>We're using Segoi UI. The Font is there and everything works fine. Then Suddenly the font is bold. If the user restarts our APP its OK.

It sounds like a bug.

Can you programmatically set the font? If so, setup a timer to check once a second to see if it's bold, and if so then reset it to not bold. Or, change the font to something else and then back again and see if that fixes it. You could also setup a function that's on a hot key and use an ON KEY LABEL to call that code so they can press Ctrl+F5 or something to reset the font if it messes up.