Note in case it wasn’t clear: this bug only happens on the OFFLINE client.
After duplicating a stash tab, the two tab’s(or more) are permanently linked. To be more clear, after tab duplication, you cannot change the duplicated tab’s priories without affecting the original tab, and vice versa. Without the ability to delete tabs, tab duplication creates a scenario where you could potentially brick your stash sorting.
While I initially thought this to be a poor game design decision, this is not the case, and does not happen on the online client.