Not sure, but you can try this-
=Month(Max(ToDate(FormatNumber([MonthID];"######"); "yyyyMM"))) + " " + FormatNumber(Max(Year(ToDate(FormatNumber([MonthID];"######");"yyyyMM")));"####")
I had bit similar requirement, so worked on it. You can refer this-
Edit: You can remove Max from the code as it is not required in your case.
Updated one-
=Month(ToDate(FormatNumber([MonthID];"######"); "yyyyMM")) + " " + FormatNumber(Year(ToDate(FormatNumber([MonthID];"######");"yyyyMM"));"####")
aniketp (BOB member since 2007-10-05)