Cognos Cube - Special date category issues

[cognosjon]

Hi
I've hit a strange one and I'm hoping that someone may be able to shed some light.
I've Cognos cube with a date dimension that was created using the date wizard. When the cube builds the special date categories are acting a little odd.
The date dimension consists of:
Year
Period
Week
Date

I'm expecting the standard MTD  and Prior MTD categories to detail something like
MTD-----Jan/2017
PMTD------Dec/2016

What I'm seeing instead is
MTD-----201701
PMTD-----201648

It appears to be removing the parent of each category.

The MTD category is simply using the Month To-Date relative time function.

Anyone come across this or have any idea what may be going on?

Thanks

[cognosjon]

It would appear that the MTD and Prior MTD will only generate the format I was expecting if the date wizard is set to be that of a Lunar Calendar.

So if I want to create a non standard date dimension ( one that isn't using the date wizard) is it possible to generate special date categories that would detail in the format

MTD---jan/2016

Prior MTD---Dec/2016

Thanks