No wireless trunk link over DFS channel with SSID broadcast off

I have vxlan over an AP-STA 5GHz wireless trunk link with a hidden SSID, but this wireless link seems to refuse to come up if the selected channel is a DFS one.

Is this behavior by design? Or would turning on SSID broadcasting alter the behavior, i.e. to allow it to come up?

If it isn't should be.

Avoid using DFS is illegal in many cases.

I should add that the same 5GHz radio using the same DFS channel serving as AP is connectable, so it means there's no radar detection and radar frenquence avoidance issue. So why can't it be used for point-to-point or point-to-multipoint wireless trunk link?

It's important to configure a country setting with your actual country in order to allow the most wifi options but also stay legal. If you leave country unset you can only use what would be legal anywhere in the world, which is quite restricted.

It should not matter if the SSID is hidden, even a hidden SSID AP broadcasts beacon packets with an empty SSID.

Running an AP and STA simultaneously on the same radio on a DFS channel is not supported by most drivers. Same for 802.11s mesh.

I have the country code set. It is a legal DFS channel where I am at. By AP-and-STA, I mean a setup like this:

openwrt #1: 5GHz AP SSID #1 for regular clients + 5GHz AP SSID #2 (hidden) for wireless trunk, both on the same DFS channel

openwrt #2: 5GHz AP SSID #3 for regular clients + 5GHz STA SSID #2 (hidden) for wireless trunk, both on the same DFS channel as openwrt #1

Regular clients can connect to openwrt #1's SSID #1 just fine (and I assume to openwrt #2's SSID #3 too), meaning no radar detected. So why can't the wireless trunk be using the same DFS channel (it's the same physical radio on each openwrt device, so it's like I could pick another channel, DFS or non-DFS)? Do you mean it should not work strictly due to the simultaneous AP and STA on the same 5GHz radio scenario on openwrt #2, but it's fine (but useless) on openwrt #1?