Time Machine w/ Dual Display

Can anyone tell me if it's normal that I have to disconnect my Cinema Display from my iMac to get Time Machine to launch? When Cinema Display is connected and Time Machine is launched, the primary display simply goes black.

It's no biggie to simply unplug the display adapter from the iMac first, but it just seems strange that it doesn't display Time Machine contents with Cinema Display connected.

Is there a fix?