Thanks Taoman! The problem is solved now. I now can see the Record button for incoming calls in the Call-Status page.
I use inbound-call-routing to route certain incoming calls to another phone number or another OBI box, then in such situation, in the Call-Status page in the (original) OBI box, the Record button only shows up in the tranferred leg, not in the initial leg. I forgot to scroll down the web page. So I missed that Record button.