I have just got hold of a 5DMK1 off ebay, great condition.

Now, I have used my 580EXII on my friends 5DMK1 before.

The problem is this, when in P mode on the camera, I change flash to manual mode, as soon as I do this on the 5D I just got it always sets Shutter speed to 200 and f22. I cannot change it.
On my friends 5D, it didn't do this, it was at 60 and f4.
Also, on my 50D it does this as well, lets you use flash in manual without changing to 200 22.

So, why on this 5D does is only let me use 200 22 when using flash in manual mode on P? It doesn't do this on 2 other camera I have tried! Am I missing a setting? I have looked all through the 5D menu & custom settings.

Totally confuddled....