On my server, when I connect a Fiber cable to the output of an MFE or BatBox, (even when connected to nothing else, just a single cabled coming out of the box) the power will be drained from the MFE at about 1K a second. However, when I use another cable, such a shielded copper cable, coming out of the MFE, the power is no longer drained. (Right now, I'm using a copper cable out of the MFE, and connecting to the rest of my power grid, which is all Fiber.)

I first noticed this in 256, and it's still happening in 264. I have not tested this in single-player, but I suspect it may also happen there.

Are you sure it isn't just the internal storage of each cable filling up? Each glass fiber has a storage of 32k I believe.

okay, WTF? I started up to take screen shots (I tested just before I posted, and this was true) but now it's not working the way I said it was... Which means it's working as intended... Without any changes...

Guess I miss-filed an issue.