By powering a piston next to a rail that eventually goes down to a lower level the rails will bug out and they will look really weird.
Steps to Reproduce:
Build just like I did in my picture.
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Confirmed in 13w02b.
Confirmed in 13w04a
Confirmed.

Is this still a concern in the latest Minecraft version 14w08a? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
Still an issue in 08a and 1.7.5
Confirmed for 14w18b.
Confirmed 14w20b
Confirmed in 1.8.1 pre-3.
IMO this should never be fixed because it allows a lot of flexibility/possibility on placing rails that is impossible when this isn't present.
Confirmed for 15w33c
Confirmed for 1.9-pre1
Confirmed.