Xbox – How to stack soul gems in the inventory to make the list smaller

I understand that some soul gems don't stack because of the size of the soul. You can't have a grand soul gem (petty) combine with a grand soul gem (grand). But sometimes my inventory has identical soul gems (with identical souls) that refuse to stack.

For example, my inventory looks like this:

Petty Soul Gem (Petty)
Petty Soul Gem (Petty) (13)

Now if I drop the 13 one, they actually drop as one soul gem, not 13 littering the floor. It's like arrows in a quiver.

My Stones of Barenziah do this too.

Can anyone tell me how to stack these into one lump?

Thanks!