The autoformat option in MBED Studio indents code by two spaces (like in Arduino IDE).
However, the tab button produces 4 spaces (which is I think the most conventional in programming).
The autoformat result does not match with normally edited code.
I would suggest to include a setting for tab definition (4 spaces by default), and apply that setting to both the auto formatter and the tab key.
On Windows 10, Mbed Studio 1.3.1