Some recent experiences:
OS op SN: book K get U (BRU-VIE)
AC op LH: book W get W (BRU-MUC) *
AC op UA: book S/V get S/V (YUL-ORD & vv) *
SK op KF: book U/K get U/K (BRU-HEL & vv) *
I've indicated on which routes observed. The * ones were credited with SAS EuroBonus, so that might end up differently with M&M, I don't know if the booking class mappings are/should be universal?