BO 5.1 Universe Designer Join display error??

Hi All,

I am looking at a Universe that was created in BO 5.1 Designer and one of the joins in the Universe looks different than the rest and not sure if it signifies anything specific.

1. All other joins are depicted next to the column on which it join in the Fact table but this one join actually points to the table header/name and not any specific column.

When I right click on this join and select properties:

Now the Expression section gives one column from the fact table joined to one column from the header table.Whereas if we look at the top then multiple columns in the Fact table are selected(shaded blue) which usually depicts that they are used on the join condition.

Can anyone explain what is happening here?is it a bug or is it actually conveying some information?

Thanks!!