I'm working on an iPhone app right now, which mostly involves dev/test against the simulator, with occasional runs on a real iPhone to check everything is running the same there. But every time I flip that menu in the XCode toolbar from Simulator to Device and hit cmd-R I spend five minutes of confusion trying to figure out things aren't working even nearly right.

After a while and maybe a bit of debugging I'll get a hunch that all is not as it seems, I'll do a complete clean and rebuild and then my code will behave perfectly, with XCode whistling cherubically with an innocent look on its face. All that remains is for me to check the Build menu to reassure myself that cmd-R does in fact do "Build and Run" which it most certainly does.

I can only assume that there is a bug in XCode that doesn't correctly reset build state when switching between targets, so it thinks my build is up to date when in fact it's ancient.