That's how it's supposed to be. This is the original feature of the game, which all players should be aware.
Extending a normal item (that will become account bound) will increase the value of their slot options, while with the new system unbinding the item these values will return to their original state.
Note: Once it's binded the extra values will be applied again.
Keeping craft level, craft option and slot option means the item will have exactly the same options applied to it but with the corresponding values (determined by the game mechanism).