What I believe happens is that the cell phone has multiple interfaces towards the carrier - one for the phone itself, and one that becomes the NAT overloaded address for HotSpot connections. If you go to a website like 'ifconfig.me' you can see that you get a different IP address depending on whether you're connecting from the phone itself or something joined to the phone by Wifi.
Unfortunately, this isn't something we can correct until we move to a system in which everyone has to login and register their hotspots. At which point, we can open up the API call to allow you to modify any of your hotspots instead of just the one coming from the same IP.
As for some potential good news, if you've built a hotspot with a usb to ttl adapter, or using one of Rob's 'TGIF' spots, I submitted some code to the team to allow for the ability to disconnect from the hotspot itself. Since the API call is then coming from the hotspot and not from the browser, it should work in scenarios like this. So keep an eye out if you've got a nextion screen with bi-directional support.