Tamás Márkus

I can relate.

Still confirmed in 1.8-pre3 with screenshot attached.

/summon FallingSand 829 4 -409 {Time:2}
Here's a command for you. Change the coordinates then use it twice and then you'll see the first block become invisible. After that you should try walking through that seemingly air block. Now try placing a block there. See?

When you load the world, the lake is solid.
Then a FallingSand entity spawns inside a block of lava. That block, in which the entity spawned, disappears visually. After a few minutes the result is as shown in the picture. Reloading the chunk makes the blocks reappear but as soon as a FallingSand entity spawns they disappear yet again.

I could summon the minecart spawner with /summon too but that doesn't change the fact that it's glitching out...

But I didn't use any damn commands man!
If even though I didn't use any commands there are commands please tell me where to look them up, because I really don't get what command you want.

I've attached a screenshot of the NBT data the spawner has. The other two compounds in SpawnPotentials are the same as the open one just with different velocities on the y axis and spawndata is one of the three. I still don't know what commands I could provide, maybe upload the filters I used but thatt doesn't matter if the outcome is the spawner whose NBT data I just now attached.

The way I made this spawner was I took a lava source, used sethbling's sandify filter on it, then on the FallingSand that filter creates I used sethbling's create spawners filter. This was all done in 1.7. After updating to the snapshot I noticed that the spawner had started spawning sand instead of lava so I took a vanilla FallingSand entity and checked it with and NBTeditor noticing that instead of the id tag in the snapshot it was using the Block tag. I then, using texelelf's NBT filter, added the Block tag to the already existing spawner. No command was used in the process so I don't know what command you want me to provide you with.