Tracking problem with .otf OpenTypes generated by Fontographer 5


Can anyone suggest why the OpenTypes I'm generating in Fontographer 5 have sporadic spacing anomalies and the tracking occasionally goes way out. It looks like I've gone insane while kerning. This weirdness is only happening in .otf font files; the .ttf , Mac PostScript and Mac TrueTypes are all exactly as designed.

If I take my Fontographer-generated .ttf file into FontLab and generate .otf files, they have the correct spacing, the problem is only in Fontographer generated OpenTypes. Am I doing something stupid or has Fontographer 5 got a glitch?

Thanks in advance.