Multebear wrote:And it works everytime. I've done it ever since I got the bike two years ago. I've even seen my LBS mechanic use that trick as well.
A few minutes reading the Shimano Di2 user manual for the SM-EW90 A/B (UM-7FE0A-002-00) and as others have already stated, that is not an auto-adjustment feature, but the crash protection recovery mode. While it is not indicating in the tech docs, I suspect the 'auto adjustment' is simply that the derailleur returns factory default spacing:
About the RD Protection function
* Rotate the front chainwheel while restoring operation after the RD Protection function has been activated.
If the bicycle receives a strong impact, the RD Protection function operates and the connection between the motor and the link is momentarily severed so that the rear derailleur will no longer operate. This is done in order to protect the system at times such as if the bicycle falls over. If this happens, press the button on junction (A) for 5 seconds or more. This will restore the connection between the motor and the link and clear the RD Protection function for the rear derailleur. If recovery cannot be performed through button operation, manual operation is also possible.
