I'm not stupid. I'm using 1.3.2 and the only mod installed is forge and the half slabs are top half-slabs placed on the top half of the blocks with no other blocks on top. This ONLY happens when forge is installed. Can you please just test it and see if you have the same problem.
As of 1.3.1, you can now place redstone wire on top of half slabs, however, I found that when I installed forge, I was unable to do so, it would simply just not put it there. I have tested this on the latest build (#246) with no other mods installed and it is still not working. I am unable to attach a log as a bug of this type does not give a log. I am using Ubuntu 12.04 LTS x64 and I guess I'm going to have to use ModLoader D:.