Some font files have some but not all subsets with characters rotated by 90 degrees. For example @Arial Unicode MS, with subset Enclosed Alphanumerics. This is not an error, but a feature of that font file. With the font rotated like this it permits writing texts in normal text editors as if they were in vertical lines.
As of version 1.13 the rotated fonts are no longer displayed in the font selection list.
Some bitmap fonts, e.g. FixedSys, may switch to Arial when generating very large fonts. This is a side effect of BMFont using GDI for rasterizing the fonts. As GDI doesn't support rendering these bitmap fonts at very large sizes it automatically switches to the default TrueType font, Arial, instead.
This happens because BMFont is a GUI application and Windows automatically returns the control to the console after initiating the application. A console application, bmfont.com, has been created to allow the execution of the tool from the command line without immediate return to the console.
For some TrueType fonts the kerning pairs that are saved into the bitmap font is obviously wrong, e.g. with duplicate entries, or offsets that are really large. This is usually a problem with the TrueType font itself, and not a bug in BMFont, as BMFont simply saves the kerning pairs it extracts from the TrueType font.
BMFont provides an option to skip the kerning pairs when saving the bitmap font, which can be used when they are defunct and unusable.
When rendering the bitmap font using the Windows native font renderer, some TrueType fonts present cropped glyphs. This happens when the TrueType font has glyphs that go above or below the fonts cell height.
To work around this, render the font from the TrueType outline instead.