I have not had any issues, so I looked at the M&M Mileage Calculator:
LUG-ZRH in P = 125 miles (156 with 25% bonus)
ZRH-JFK in Q = 3919 miles (4899 with 25% bonus)
If your ticket is return with the same booking class your assumption is correct.
I do around 60-70 segments a year on LX, LH, and other Star carriers. I can’t remember getting the wrong miles, just not posted at all which happens once or twice a year.
I would do the following:
1. Use the online credit system and submit as “missing” miles to see if it corrects the error
2. If this doesn’t work, call your local M&M Service centre
3. If not, send a message to the service centre.
I find all of them very responsive.