It seems to be rune-specific (at least for me so far), and it started within the last 2-3 days:
I have several instances of same-kind runes that will take up 2 slots while I have approximately 10 to 20 or so of these same-kind runes in each stack. They won't combine.
I have a single stack of 'Ta', with 87 items in it, so I know they do stack 'that high'.
I'll have 2 stacks of Porade (As just one example of several runes I have doing this). One with 11 items, the one next to it with 23 items.
Edited in response to: Daverios.
I see a problem here.
I mis-remembered, and thought it was 23.
It is in fact '20', and had no knowledge of there being a limit of '20' in a stack.
It is indeed 20 and not '23'.
I needed to get my facts in a better pile before I posted, I started without enough coffee this AM.
Currently:
I have a stack of EDODE with '1', next to a stack of EDODE with '3'.
I have a stack of JAYDE with '1' next to a stack of JAYDE with '12'
I have a stack of NOTADE with '7' next to a stack of NOTADE with '20'.
I have a stack of ODE with '1' next to a stack of ODE with '20'.
I have a stack of ODRA with '3' in it next to a stack of ODRA with '5' in it.
I have a stack (now) of PORADE with '16' in it next to a stack of PORADE with '20'.
I had several other stacks that I have not yet gotten back from friends.
End of edit.
I can sell both stacks to a vendor, and they stay separate.
I can buy both stacks back and they stay separate.
I can mail them to a friend and he can't combine them.
I can log off/on several times....
I can put them in my bank....
I can restart the game....
And they stay separate.
Right now I'm using 6 extra slots on my gathering/enchanting 'toon because of double stacks.
No one I've spoken to yet has, or has heard of, this issue.
I'm asking you guys.
Edited by twev on 2 May 2014 15:00 The problem with society these days is that no one drinks from the skulls of their enemies anymore.