I found this by accidentally right-clicking on some of my cabling. 
If you use TMI, you may have noticed a strange "Unnamed" item at #228 (next to another "unnamed" at 229, I might add). This 228 is the item that drops if you use the wrench on insulated copper cables, and also on 2xinsulated gold cables. I haven't tested with fibres or HV cable. When this first happened, I was like, "lolwut?" and immediately tried to place it in the world; lo and behold, it turned into an insulated copper cable that I could break (with my fist this time) and pick up the item version of. So, no harm, no foul. But, rightclicking a gold cable will also drop the same item, which you can then place and break, but you recieve a COPPER cable again, not the gold. Your gold cable just got magically turned into a copper one. 
It's not gamebreaking, and MC didn't crash, but it's obviously something that shouldn't be happening.
If I may go out on a limb here, perhaps this is something left over from IC1? the sprite for 228 looks alot like the old-style cables... but that's just a guess.