Thanks, fewi. I was looking for that earlier.
May I suggest to the MT crew to modify the wiki to include the warning about Universal NAT and arp poisoning. If a user wishes to allow connections to other localnet users behind the hotspot interface, disable the Universal NAT. Maybe something like this in the manual under hotspot:
address-pool (name / none; default: none) : address space used to change HotSpot client any IP address to a valid address. Useful for providing public network access to mobile clients that are not willing to change their networking settings. However, the Universal NAT uses arp poisoning, so in order to allow localnet computers behind the hotspot interface to communicate with each other, the address-pool should be set to none (disables Universal NAT).