Darn hard to tell, but I think it is more or less normal. What you have is a stereo graphic, one side of which can be assigned to either main or AUX1. By its nature when on AUX1, that side of the graphic cannot be also in the main line. The switching is pretty involved. I THINK the way it works is in MAIN mode it is straight stereo. In AUX1 mode, the EQ works on the MONO channel and the AUX1 channel.
But I really don't expect my main L/R outs to lose one side. SO I would get some cleaner into the MAIN/AUX switch, and the EQ IN/OUT switch