AntiShare: 5.4.0 Build 212
CraftBukkit: 1.4.7-r1.0-B2624jnks
Config: http://pastebin.com/mhbNABJz
To replica this would be a lot to type, and you probably wont understand it so here is a youtube video on how to make it.
http://www.youtube.com/watch?v=PIMJEyw77bg

The problem I'm having is the pistons wont move pumpkins or melons. When I had antishare enabled, once the pistons touch the melon, the melons disappear.
And when I have antishare disabled it works fine.

Are the melons creative blocks?

Use a blaze rod, as OP, and hit the melons to find out.

No they are not creative, I had the player rebuild it in survival to make sure that wasn't the problem, it didn't work. I just redid it myself with the blaze rod and it said "That melon block is a natural block"

I can confirm this in the beta, and only the beta.

For whatever reason the beta has this bug but 5.3.0 and the latest development builds do not.

TL;DR: Already fixed for the next version