Monster Spawners in dungeons fail to show the mob its meant to spawn

Upon finding a mob spawner in survival on peaceful, I had found that the spawner did not contain the model of the mob it was meant to spawn. Though I was confused, I assumed it was a one-time thing, so I continued searching cave systems until I encountered another spawner with the same problem. I decided that I'd attempt to investigate further and see whether it was just a bug when on peaceful survival mode, thinking that the game didn't bother to put the model in the spawner because no hostile mobs of its kind can spawn in peaceful. I went into my game settings and put the difficulty on hard, but the visuals were still incorrect. I then made a copy of my world and set it to creative to see if it occurred even when the mob spawner was modified by the player by using a spawn egg, but the results were still the same. That had all been about two weeks ago, but today, while encountering one of the two previous spawners once more in the original version of the world, I had found that when higlighting the block or pressing the screen as if the goal were to mine it, the model for the mob would appear within the spawner block, but the moment the finger was removed from the block, it disappeared once more. Though it's no game-breaking bug, I felt it was still worth reporting, as I'm sure it wasn't an intended addition to the game.