It seems that AS needs to publish a full manual of how zeros should be added to FF# for each partner airline!

I decided to take the retroclaim path, despite the concern that miles may unexpectedly show up in BA account (It didn't).

I sent an email to Mileage Plan and described the problem with number of digits of FF# and even attached a photo taken from the computer screen of check-in agent at LIS. I clearly asked what I need to do to prevent this problem in future.
Mileage Plan replied with an irrelevant message asking me to send them the e-ticket and one BP to credit miles. As if I had asked how to credit miles!