Curved rails switch orientation when redstone receives an update (whether it is broken or powered). This occurs even when the redstone is unattached as seen in following setup:

This does not happen if the redstone is switched to the "dot" form or with solid blocks, but happens upon placing, removing, or updating any redstone component pointing at the rail (eg a repeater will cause the update only if it is pointing towards the rail). This only occurs when the top of the setup is facing either east or south and not west or north, probably because the rail is in its preferred direction already.

Steps to reproduce

• Simply build the bottom half of the setup first (to arrange the curved rail in that direction) then place the two rails above.
• Place either redstone dust or a repeater facing towards the rails and either power it or break it.
• Observe that the rail will change orientation