[illuminant]

I've noticed this phenomenon of disappearing posts as well.

There are "flagged" posts, which say [flagged] and then there are disappearing posts which just, disappear!

I have had such posts open in separate tabs, and when refreshed they and their content show up blank.

[pvg]

They don't, unless the poster deletes them and that only works if there are no comments (for story posts) or replies (for comments).

Go to your profile and check the 'showdead' checkbox. You will see more crappy things but if that's what you want, they'll be visible to you.