Soft start may be disabled until the motor is completely stopped for 3 seconds (read that in my ESC manual). I quote from the Thunder Power manual:

http://www.rctoys.com/pdf/thunder-po...esc-manual.pdf

'The initial speeds of Soft and Very-Soft mode are very slow, usually it takes about 1 second (Soft startup) or 2 seconds (Very-Soft startup) from startup to full speed. But if throttle is closed (throttle stick moved to bottom) and opened again (throttle stick moved up) within 3 seconds after the first startup, the restart-up will be temporarily changed to normal mode to lesson the chances of crash caused by slow throttle response in aerobatic flying.'