Power sources keep a list of things they are powering and recalulate this list whenever they recieve a certain type of update to a block they're powering. This is done for performance reasons and makes redstone dust and redstone in general way less laggy than java for the most part.

However, they calculate this list around 10x slower on a block update than they do when the chunk they're in is first loaded. I don't see why this should be the case. It shouldn't be that much slower. It should be faster actually.

As well as this, it recalculates everything it's powering, instead of only checking the section that got the update.

It needs to be way less laggy than it currently is, because the current behaviour allows for some really compact lag machines, such as this one, which can bring a server to it's knees in under half a subchunk of space.

I'll send a test world soon.