Shutter speed and All Reset.
 

Just a bit of a heads up. The All Reset resets the shutter speed to 1/100th. The only way to get 1/50 is by setting Shutter to Angle at 180deg. I know this got discussed way back and there was some hope this would get fixed in new firmware but not so it would seem.
The curious thing is that even when set to 180deg in 50i the greyed out speed still shows 1/100.
Why I really noticed this was a few days ago I was the tech support for a 3 cam EX1 shoot. We had my camera and two rentals both of which were set to 1/100 out of the box. It's common practise for a rental company to do a hard reset on a camera to get it back to the factory defaults and that along with default Auto setting for Flicker can be a problem.

But 180 degrees at 50i is actually 1/100th. I.E. 180 degrees = half. Half of 1/50th(50i) is 1/100th.

You don't have a 1/50th shutter at 50i as that would be the same as shutter off. That's why the default shutter is 1/100th. It's not a bug, but how it should be.

I think shutter speed / angle is based on frame not field rate. I'll admit what you're saying did enter my head however checking elsewhere confirms what I've always believed. The 'standard' shutter speed for 50i is 1/50 and for 60i, 1/60. The EX does have a shutter speed of 1/60, no doubt for 60i.