The MY12 models have a few software bugs in the GOM display/Mode selection - you've just hit one of them. When it totally runs out of electricity in Normal mode, it switches to ICE, and you know all about that! You then decide you want to build up a bit of a reserve so you can leccy through the next village you come to, so you select MM to do this. Which it will. Ice revs away & is genuinely charging the battery, but for some bizarre reason you can't now switch back to Normal mode and see what Ev range you have! You may have added 3 miles to your Ev range, or maybe 8, or whatever, but it won't let you see! The only way to find out is to stop the car, switch off, switch back on, and lo & behold, you can see Normal mode with 3 or 8 or whatever miles you have in hand. Why it won't let you flip back easily is a bug imho.
When you're in MM mode, the car likes to keep a much larger battery reserve, = 1/3 the capacity, so around 15 miles worth. E.g, if in Normal mode with 35 miles range showing, try switching to MM - it will immediately deduct about 15 miles and show you 20 left! So in the earlier scenario above, it seems that while you're in MM mode, as far as the car's concerned, you're in negative territory (!!) as far as the car's concerned, and you have insufficient leccy to be in that mode so it's not going to get your hopes too high by displaying miles you're not going to get because you're just about to drive up the north face of the Eiger or something!
It's a bit stroppy if you get below 5 miles left in Normal mode - at any time it's likely to display the engine & gallons left, although still actually working in Normal mode under the covers draining leccy. So switch to Hold mode with <5 miles left, and you probably can't get out of that easily. So I make sure I do all my Normal/Hold flipping with >5 miles remaining.
Here's another slight niggle - the petrol gauge. Ice miles remaining is decently shown - but if you get low, the display flips with <50 miles left in the tank, it then displays a low fuel message & periodically pings at you reminding you to fins a petrol station, but you now can't see how many petrol miles remain! So if you're squeezing the tank to almost empty, you need to note the miles-gone when it switches to the warning message, and after that you have to work out from the odometer how many Ice miles are left in the tank. Easiest thing is to avoid getting that low.