Originally posted by umop-apisdn:

Originally posted by _I_:

any mods?

Very insightful! Mods render any and all arguments about whether (and how) vanilla mechanics work utterly moot.

I mean, yes. That is how it works.
Items don't just vanish. There can be errors such as the world failing to save properly. In that case a chest may have forgotten the latest change to its contents. Items do not delete on their own, however.

If you're playing with friends, 9 times out of 10 look out for their smug grin.