I've found a few threads on an issue similar to this scattered around the forums, but most were old and none seemed to really go anywhere solution-wise—nor did they have as straightforward a scenario as this. Here's what's going on, conveniently summarized in three easy steps:
Other relevant facts:
Since some of the similar questions in this forum are from way back in 2012, this is clearly not a new issue. I would hope that this means it's not an unaddressed Lightroom bug (since I have faith that the developers would have noticed and fixed such "image-disappearing" behavior by now) and instead has something to do with the files themselves or the way they're loaded into the catalog.
So...any thoughts? Better yet: any solutions?