I was playing around on creative on an AMPLIFIED world and came across this bug. I have included a photo. It looks like one of the redstone torches on the repeater turns into a part of bedrock.
MC-42425
Redstone repeters
Resolved
Duplicate
0
Adam Tomaszewski
(Unassigned)
Unconfirmed
Minecraft 1.7.4
Retrieved
Not a bug, please reference the wiki. While not a validation source it lets you know how the game functions.
http://minecraft.gamepedia.com/Redstone_Repeater#Signal_locking