Correct me if I'm wrong, but wouldn't using actuators fix this?Sand, Silt and Slush now destroys cobwebs, which broke a lot of contraptions in adventure maps. Although it looks like from my testings, that it only happens when the player goes relatively close into it's vicinity, so it might be possible to fix this, by placing the sand and cobwebs in TEdit much higher up.
I do have to say though, the 1.3.1 update gave a lot of content to help with adventure maps and wiring, but 1.4 is doing the opposite now...
Now I'm curious, can this method be used to remove a large chunk of sand quickly (by placing a layer of blocks below the blocks that support the sand, and actuating the support layer)?Also, if the bottom block is the one being actuated, and there is another block below that, the sand block will just drop down as an item, that's how they solved it.
1.4 update changed the sand mechanics which broke a lot of pre-1.4 adventure maps. While I'm not sure if this is a case of broken sand mechanics, there are other areas that don't work anymore as far as I remember. If you want to play this map I'd suggest playing in an older version of Terraria