The redstone block ¹ should have partial opacity, meaning that mobs can spawn on it, but ladders can't be placed on it, for example. However there are some discrepancies between the redstone block in MCPE and that in PC/java, where the redstone block is still behaving like a fully opaque block.

The incorrect behaviours in Pocket Edition are:

• Ladders can be placed on the sides ²
• Minecarts bounce off redstone blocks ³
• Chests placed underneath cannot be opened

(Keep updated with any further info)

References
1. http://minecraft.gamepedia.com/Block_of_Redstone
2. MC-5850
3. MC-6311