Quite normal. I was on a project commuting MLA – FRA – CPH every week. The MLA – FRA leg was operated by KM and the FRA – CPH leg by SAS but, they both had code shares with LH. So I had four ticketing options:
KM/LH
KM/SAS
LH/LH
LH/SAS
The prices were different for each combination every week and it wasn’t one combination that was always the cheapest. Block booking tickets was a nightmare. I had to do a spreadsheet to work out the cheapest ticketing option for each week!