Hello! This is a redo of issue #231, which was abandoned by the poster. I am not familiar with Github etiquette, so please excuse any mistakes. :)

I am unable to place microblock slabs, panels, or covers on the sides or top of a length of alloy wire. The microblock placement overlay UI acts as if the wire is a solid block. Attempting to 'split' two adjacent wires as shown in the wire wiki page (fourth picture: http://projectredwiki.com/wiki/Wire#Flat_Wires ) acts the same way, as if both are solid blocks. The same problem happens with insulated, bundled, framed, and insulated framed wires.

I first had this problem on a friend's SMP server running Minecraft 1.6.4 and Forge 9.11.1.965, with several different mods in addition to PR and FMP. I pared them down to test in single player, ending up with the following list:

.minecraft\mods\1.6.4\CodeChickenLib-universal-1.6.4-1.0.0.62.jar
.minecraft\mods\1.6.4\ForgeMultipart-universal-1.6.4-1.0.0.244.jar
.minecraft\mods\ic2\ejml-0.23.jar
.minecraft\mods\CodeChickenCore 0.9.0.9.jar
.minecraft\mods\immibis-core-57.2.0.jar
.minecraft\mods\immibis-microblocks-57.6.3.jar
.minecraft\mods\industrialcraft-2_2.0.397-experimental.jar
.minecraft\mods\ProjectRedBase-1.6.4-4.3.7.32.jar
.minecraft\mods\ProjectRedCompat-1.6.4-4.3.7.32.jar
.minecraft\mods\ProjectRedIntegration-1.6.4-4.3.7.32.jar
.minecraft\mods\ProjectRedLighting-1.6.4-4.3.7.32.jar
.minecraft\mods\ProjectRedMechanical-BETA-1.6.4-4.3.7.32.jar

Removing the IC2e jar and directory made Minecraft crash on load, so I don't know what else they're interacting with. I can post the crash report if it would help. I can also post screenshots if need be.

Please tell me any other info you need. Thanks for your help!

I think I have found your problem.
After setting up an identical setup to your configuration (I also added NEI)
Placed some wire down, went into NEI, grabbed any cover from FMP (Forge Multipart) tried to split wires, it worked.
So, I thought, what could the problem be.
You have immibis-microblocks.
Turns out Immibis's Microblocks also implements a similar system to Forge Multipart and that ProjectRed only has support for FMP.
The slabs, panels etc you're using were created from Immibis's Microblocks via the Hacksaw.
You will need to convert panels etc back into solid blocks and then use a Saw eg Diamond Saw which comes from FMP.
IMO FMP is superior to Immibis's microblocks, unless another mod requires it I suggest removing microblocks.

Thanks! Yes, I was using the hacksaw microblocks, and didn't know they were different. I think we needed Immibis for something else, but I'll tell everyone to use the FMP microblocks with our wires.