>>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.

Does this happen if antialiasing is disabled? I vaguely recall there could be a problem when antialiasing is used and you have text with transparent background -- this could result increasing "smudginess" with each redraw and text ends up appearing bolded as a result.