Mineral/herb bags: 3 max?

I wanted to open a bag but got the message "the bag could not be opened again."

At first I thought you could only have one bag of the same kind open, but this was not the case. It was a 6 slot bag and I had two 4 slots and a 8 slot open.

So I guess 3 is the max amount of bags you can have open.

Can anybody confirm that if I throw away the 4 slot bag, I can open my 6 slots one?