It is documented here on the wiki due to being officially-released content by Mojang Studios, even if not present in a final version.
|Catches fire from lava||
Punching the block breaks it instantly and it drops in item form.
Etho slabs are crafted using 3 TNT blocks.
Blocks with data value 1 are called "Etho Slab (Lit??)" and explode on punch.
|Name||Numeric ID||Form||Translation key|
|Double Etho Slab||Block|
|Etho Slab||Block & Item|
|1 (0x1)||If this bit is set, the Etho slab is triggered on punch rather than destroyed.|
|4 (0x8)||If this bit is set, the Etho slab is a top slab.|
"Etho Slab" is an April Fools feature, and as such issues related to it cannot be fixed.