When you try to rename all occurrences of the group from the kerning window, it only renames it for the current master. It seems like it should go through all masters though, since the glyphs’ groups are renamed too, and so the glyphs end up with no kerning in other masters.
I was about to report the same. This feature renames the kerning group of the glyphs in the font as well as the kerning entry in the current master only. I want it to do the job in all masters.