Hello, Isaaс!
It’s really misterious. I never met such complains.
Is this MO CDR originall meaning directly from MSC or provided by billing department? Maybe some mistake after processing in billing?
Other thing that you can define any MSISDN for IMSI in HLR and it does not affect on mobile-originated call, so you can clarify this with IMSI operator, maybe really wrong MSISDN defined.