iOS Simulator oddness

[Graham Samuel]

I've been doing some testing on an iPhone app on my newish iMac. The simulator has been working as expected. I'm now on a trip and have switched to my MacBook which AFAIK has the same development software (LC 5.5, XCode 4.2.1, Simulator 5.0 etc) - but now the simulator insists on opening in iPad portrait mode, with my app in the middle of the screen - exactly as happens when you open an iPod/iPhone app on a real iPad. If I switch the simulator to iPhone, my simulated app disappears. I can't get the simulator to open in iPhone mode.

I imagine I have done something wrong with the standalone settings of my app, but what? Can anyone suggest what's happening?

TIA

Graham