Powered rails exhibit the following unexpected behaviors when being powered by Redstone Blocks and Torches:

1. Placing a block to power a segment of rails and then placing another block to power a rail that is already powered will not extend the distance of the powered segment. (Also happens with Torches placed anywhere except the last active rail in the segment)

2. Under certain conditions, removing a redstone block or torch as a power source will not remove power from the rails, if there is still at least one power source in the active segment.

To test, place a long line of powered rails (at least 20) then place a redstone block or torch next to the first one. Place a torch next to the second-to-last active rail. No additional rails will activate. Remove the torch and place it next to the last active rail. Rails will activate out to the expected distance from the torch. Re-add the previously removed torch, then remove both torches starting with the far torch. The rails will remain powered until all power sources are removed.

Repeat the test with blocks instead of torches, with the second block being placed next to the last active rail instead of the second-to-last rail.

This can be extended for a considerable distance as well as up and down slopes.