RAX45 Cannot change 5GHz from long preamble to short preamble

I recently acquired a Netgear RAX45 at Costco. I setup the router, however I cannot change the 5GHz band from using long preamble to use short preamble.

I can select short preamble, in theory save it, but when the router restarts is is still on long preamble mode. The firmware version I am using is V1.0.4.100_2.0.64.

I searched the Netgear community and I have seen other models with similar issue (RAX80 is an example). This problem requires a fix since the ability to operate on the 5GHz band with short preamble is part of the 802.11 standards.

Thanks.