Repeaters do weird BUDdy things (This works with comparators too)...
budwut0.png: Make a simple repeater circuit. You must have redstone running into a block with a repeater out of the block on the opposite side.
budwut1.png: Add a repeater to redirect the redstone away from the block. The other repeater is now a BUD.
budwut2.png: Update the repeater to prove it's a BUD.
budwut3.png: Clean up any mess you made while updating the repeater and remove the redirecting repeater. The repeater is a BUD again.
budwut4.png: Prove repeater is BUD.
Maybe redirecting redstone should create a redstone update...? (IMO, BUDs should be impossible. They're symptoms of updates not being sent when they should...)
It is because you added redstone that couldn't be detected that far away.