[Microbit-Python] Copying python scripts to the microbit.

[fresh.bread]

I'm  figuring out how to program the microbit in python but am finding 
the differences between the pyboard and the microbit confusing.

I was under the impression that I could use uflash to flash a python 
runtime system (what I understand to be a python interpreter) to the 
board. If I do this I can open a terminal on the board and execute lines 
of python,[ tick!]

On the pyboard, if I copy a python script to the board as main.py and 
then reboot  the board, it will run the script

On a microbit, (that I have flashed the python runtime using uflash), if 
I copy the main.py and do a soft reboot (i.e ctrl-d or use the reset 
switch) the script does not run. More confusing, if I do a hard reset by 
disconnecting and reconnecting the microbit, the main.py on the microbit 
vanishes? Is this normal?

[The differences won't stop me programming the microbit its just that I 
would like a similar approach for both boards if that is possible]