Bukkit

What steps will reproduce the problem?
1. Install
2. Craft two backpacks of same kind
3.  Try to stack them

What is the expected output? What do you see instead?
I expect the backpacks unable to be stackable.
Instead the backpacks will stack, but when trying to seperate them again, you lose everyone of them except 1 of them

What version of the product are you using?
v1.6

Do you have an error log of what happened?
No error log

Please provide any additional information below.
I have never used this plugin before and we did our testing with the default/example backpack provided...

We kept trying and trying to repeat this bug over and over again and each time they would stack, but they wouldn't separate without losing all but one.
If in creative while trying to do this test, the chests will separate as though you're pulling another chest out of the creative menu.

I can separate stacked backpacks just fine by right clicking in empty inventory space, how are you trying to separate them?

By right clicking on the stack from my inventory screen, just like i separate everything else.

Personally, I don't think backpacks should be stack-able at all.

Considering these are items designed to extend or expand the inventory space a player has to travel with, i see no reason that the backpacks need be able to stack up with one another.

Yeh, I've been planning on making backpacks unstackable but it takes awhile to make custom items unstackable over regular items since I have to make custom methods for every event a player can stack a item. And when doing something like this, it is very buggy.

Oh my, sounds like quite a pain. Well then, I look forward to you getting this working properly and will use it as is in the mean time :3 I will just make a note to notify players not to stack them as right clicking empty space is not something you normally do to separate things.