This seems to be pretty simple:
I was testing how much miners a LV Transformer could supply when this happened.
One of said miners started to mine the pipe head (or "drill") of the one next to it.
Reproduce the bug:
The miners are placed next to each other.
It's not a setup that you would usually choose, since it's not such a good idea to place them that close together. Even if it's bogus, such a setup would still occur if you, for example, count wrong and place multiple miners to close to each other.
In my setup I placed them with a one block distance next to each other.
You might need some more miners, since the chance, that one miner mines the others pipe head is very small.
Also all miners have to be at the same level.
There are 2 screenshots in the attachment. One shows the pipe heads in the chest, the other the miner setup.
Again it's very unlikely to happen. It also does "not really" affect the gameplay, which is why it's only a class c bug.
But still, I guess the pipe head is not supposed to be inside of any inventory ever.
Also one pipe would be lost, because it's impossible to place that block, either.
I believe it's kinda hard to fix that bug, I mean, what would you do?
It could be possible to cause the miner to stop, just like it does when finding water or lava.
As soon as the other miner mines further, the stopped one would continue either.
I hope I could help, HAYO!
Other mods, of course, are:
BC 2.2.5, RedPower2 pr3, BC<->IC Power Converters, IC Addon: Thermometer
(Only tested in SSP, since a SMP test would use modified code on my side (bukkit port))