Shelf changesets limit

Hi!

Do shelf change sets expire? Or are there a limited amount of them kept? I am in the habit of storing lots and lots of changes there so that if I am in the need in the future, I can go back and get them.

There used to be no limit as to how many I could keep. But recently, it seems that some older ones are gone (though I am not 100% sure).

Is there a limit or am I misremembering what I shelved? If there is a limit, it configurable?

Thanks!