A spawner cart will always show a spinning pig, regardless of what it spawns. So far, I've only tested it with mobs and monsters.
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There are so many features that were added to be just accessible via 3rd party programs, but just because of that, you can't say they don't need to be fixed! These are official features and need to be fixed, no matter if accessible or not!

Is this still a concern in the current Minecraft version 1.7.4 / Launcher version 1.3.9 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
I think you can /summon them. I have a command block set up that does that.
you can, /summon MinecartSpawner

Is this still a concern in the current Minecraft version 1.8.1 Prerelease 3 / Launcher version 1.5.3 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
resolving to MC-65065
The spawner cart is not available without using 3rd party software or mods, so it might be invalid ticket.