This happens every time I make a kern exception for glyphs with an attached ogonek. Often I have to make a kern exception for Aogonek followed by j. That is fine, however if I work on the kerning of another master in the file, I find on going back to the first master that the Aogonek j kern value is no longer an exception and the class A first to j has the value that was previously the exception value.
To get around this problem I now copy the kerning from each master and store it separately in a text file for when I export, when I paste the kerning back in to the kerning window, to make sure I am getting correct kerning.
Is this a bug or is there something I’m doing wrong?