ACD 23" Alu not displaying out from a fresh boot

my cheesegrater MacPro recently died on me so I've "relegated" the ACD to work with my rMBP through the thunderbolt port with an Apple minidisplay-DVI adaptor

Magsafe adaptor is on so the rMBP is closed and used with an external keyboard/mouse

Everything is working perfectly if I boot up the rMBP then connect the ACD to it

What's not OK is when I power on the rMBP with the ACD attached. it doesnt display out anything.

The rMBP does recognise the ACD with a quick pulling out of the adaptor from the rMBP then back in again. But there is no display on the ACD. the ACD and the rMBP goes into spanning mode as the mouse moves out from the rMBP to the blanked out secondary display (ACD)

My solution now is to connect the ACD only when the rMBP is up and running. The ACD has to be powered off from the powerplug and reconnecting the adaptor again which is silly.

how can i use the ACD properly without hotpluggin