string themeName = "Office";
ThemeFontScheme themeFontScheme = PredefinedThemeSchemes.FontSchemes.FirstOrDefault(x => x.Name == themeName);
ThemeColorScheme themeColors = PredefinedThemeSchemes.ColorSchemes.FirstOrDefault(x => x.Name == themeName);
DocumentTheme theme = new DocumentTheme(themeName, themeColors, themeFontScheme);
Setting SetIsBold method to true on a CellSelection, resets the font size of those cells to 11 points.
See the generated file of the attached program.
Cells C1:F1 have font size 11 instead of expected 9.
PS: Is it really necessary to have a support plan to report bugs?
Filter Selection dialog appears on the screen.
Workaround: Open the file with Excel and save it as a new document.