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?