I noticed when I was adding kerning to intermediate masters that exceptions were being left behind. Could you have a look?
semi relevant to this…
i personal wish i could reinterpolate not only the outlines
(via the cogwheel menu in the layertab) but also the kerning,
for intermediate or normal master layers…
Semi-relevant to this, Kernschmelze unfortunately fails to interpolate exceptions it seems, and resets source exception values to zero, as I raised an issue on the repository.
As I wrote at this issue over at Github: writing the zero values is crucial to make an interpolation work. you cannot interpolate something between a value and nothing. Well, you could treat the nothing as a zero, but that’s just a patch either way.
But as I also wrote there: I’ll check what’s going on with the exceptions there. It doesn’t sound to me like sth. that should happen. I wonder. Anyway, it’s open source, so you could peek into the code and double check. I surely make mistakes from time to time 
Yes, I’ll send you a file later.
Regarding the zero issue, since the source masters are only two, the interpolation should be easy enough to do independently rather than modifying source masters and the let Glyphs interpolate.
Exceptions are supposed to be interpolated on export. If not, then I would like to see the file.
Consider three master setup and you have kerned two extreme masters. You get an instance as working file (by removing the mid master first of course), then copy & paste its kerning data back to the original file. This kerning data does not contain exception anymore.
I’m so sorry Mark, I now cannot reproduce the result. Please consider it closed until I can.
I also discovered that the interpolation of exceptions fail in python (interpolatedFont).
I still haven’t managed to reproduce it. Speaking of kerning, contextual kerning is still being ignored. Could you fix that please?
Can you send me a sample of the not working contextual kerning?
Thanks for the file. I fixed it.