This happens in both Survival and Creative. If you power a redstone repeater sideways (facing either North or South to a East or West, or vice versa) and the redstone repeater going to the sideways repeater has to be powered.
Will include a photo (shown below)
This is on the Minecraft 1.5.1 Pre-release, not the snapshots.
Environment
Win 7 x64 and also tested on Win XP
Latest Java version for x64 (unknown right now, not at the main specified computer)
Duplicate of MC-4449, please use the search function to see if your bug has already been submitted. Currently over 54% of tickets are being closed as duplicate.