I'm running ICS 2.4.20. What internal memory stats do you have? I have Total 2.87 and available 2.60 GB. I thought this phone should have 4 gb rom? Or is part of the 4 gb used for something else?
Well there is always a small amount taken for the system, but I know its not 2gb worth. How many apps do you have installed locally? I bet something has a big cache is filling up your space.
I don't own an Mi One, but I remember that it has 2 bays for ROMs, so you can sideload one while you update the other. This usage probably accounts for that space, but we'll wait for Mark for an official answer. As he owns an Mi One.