GNP has been like this for years. This is not just D-Link but other router mfrs as well. All this is set forth by the wifi standards that router mfrs have to follow.
Maybe your devices your using and environment are problematic, not reading correctly the channel width or your router needs replacing.
I haven't had any issues with using D-Link routers and the GNP. Works well when setup well.
Good Luck.