As I work on several digital boards in live sound, I first assumed that this was a software failiure of a SL series 3 owned by a customer of mine, since the GEQ inserted on a subroup did not seem to work. After I checked this on a few other SL series 3 consoles, I found out this is appearantly by design.
As I said: I kind of need a GEG inserted in subgroups, since I use the board in a situation with speakers wearing headsets in the style of DPA 4066 mics. DPA's are rather easy to control, but 'more affordable' mics of that kind do need some work to prevent feedback when a person wearing it moves around in the room and gets in front of the main speakers.
Please get this fixed.