Membership Category "None"

Hi everyone!

Has anyone come across the membership category "None" before?  It only seems to be an issue in the Contributions cube.  We've created a widget that just breaks down YTD contributions across various funds etc, and I've created a jump to that splits things out by membership category.

This is how they appear in that jump to:

However, if I create a similar widget using the Membership cube, those same constituents are accurately placed in their correct category:

All of these people do have a current and active membership for the current fiscal year, so I'm thinking it's something to do with the way the Contributions cube looks at memberships.  Any help is appreciated.

Thanks!