Are people actually losing their whole post or just not seeing it after the initial posting?

I've never seen this happen to my posts but people keep saying it when in fact I can see their post right there. On the other hand I have seen it said when the post in question only shows a title.

So can I have some clarification:
(a) On the nature of these disappearing posts
(b) On the browser in use when they disappear

Cheers