That's what I assume is happening also. There is no way to disable the integrated chip on the cpu through the bios. Also when right clicking on the catalysis control center it shows the integrated chip, but not the dedicated graphics card.
I would have thought the HDMI port would be for the dedicated card and the mini port from the motherboard. Worth a try but if it worked perfectly well before it might mean driver problems. Whatever, if the mini port works as well then the card is functioning. See what happens.
If just as bad then connect back to the HDMI port, open CCC, select 'information' on left, AMD Home, untick 'Allow Web Content' then click on 'check for driver update'. If the latest is installed then I'd try going to device manger and rolling back the driver. It's a puzzle this one.