Client connects at rates not allowed

Clients have their supported and basic rates set to ´default
AP has Data Rates set to configured and only basic and supported are set to 36Mbps.

If I look in the register table of the client, is shows the signal strenght of the 36mbps only.
If I look in the register table of the AP, it shows for almost all clients both 36 and 54Mbs signal strenght!

How is this possible?

All MT routerboards with MT radio’s running v5.4 latest firmware in 5ghz band-10mhz wide and NV2 protocol.

any ideas?
Conn rate.JPG

Nobody?

Has nobody seen this?
Can nobody reproduce this?

This looks very weird to me, basically impossible…