On occasion I've seen posts get deleted with no reason listed on the uploader's Deleted Posts page, and the post page itself displaying "This post was deleted. Reason: . MD5: <i>(string)</i>".

- Recent example: post #74155

What's the explanation of this kind of deletion, exactly?

In that example, Kamicheetah a.k.a Aja Williams is now on the Avoid Posting list.

Ah, okay then. I'd wondered if that was the case, considering I checked them and suddenly 235+ images were listed but only 13 were showing. Do those 13 have extenuating circumstances or something?

the do not post list can be foud here in case you want to memorize it http://e621.net/wiki/show?title=avoid_posting