Mine has come on when I have had 2 bars, 1 bar and a flashing bar. It also has switched off then come back on later on. Is this normal?
The US owner's manual says it shouldn't come on until the bar starts flashing. Mine's only come on once so far - had reasons to top up earlier, the other times - but it was at the same time the bar started flashing. If you actually plan to rely on that, I'd have it checked. Might have it checked even if you don't plan to rely on it, you kind of never know with electrical glitches whether they'll stay minor or whether it might be a bad ground that could involve other components.
If it's a float gauge like most of them, yep it's normal (just as in any other vehicle) that acceleration, deceleration, leaning, climbing or descending can all change the level of the float and thus the fuel display. But, as far as I can tell from the manual, the reserve gauge and the flashing bar should be tied together.