Originally Posted by PatriceJ

look at it another way ...

once you have purchased Case #2, you'll find the first. then you'll have one to use with regular thread and another you can use for specialty threads.

you'll always have your tension right for regular threads and can fiddle with the tension on the other without worrying about resetting it properly for regular thread.

this little inconvenience is really "cosmic permission" to buy a spare case. you would probably not have allowed yourself the luxury otherwise. ;-)