Should USB3-3900 DHE graphics adapter work in non-charging ports of 7-port Plugable USB3-HUB7-81X?

I bought two Plugable Dual Head USB 3.0 graphics adapters (USB3-3900 DHE) and want to connect them to my Acer Win 10 laptop through a Plugable USB3-HUB7-81X 7-port powered hub.

I am finding that the Dual Head adapters (and connected monitors) will only be recognized when using the two outboard “charging” ports on the hub. The inner ports give intermittent results, usually with no connection. I was fairly certain that the main requirement for successful connection through a USB hub was that it was a powered hub which the USB3-HUB7-81X certainly is.

I’ve already submitted a support request ticket (#165615) awaiting first reponse, but just wanted to know if my expectations were correct or misguided.