In previous versions (up through 1.7.4, and 1.8 snapshots through 14w05b), a Comparator would read and output a signal from a Minecart with Chest/Hopper if the cart was on a Detector Rail, even if the rail was sloped.

Starting with 14w06a, this no longer works if the cart is on a sloped detector rail, unless it is on the very bottom end of the rail. This behavior can be seen in the attached pictures (the lower, sideways comparator; ignore the higher one).

This breaks several redstone contraptions, including many automatic cart loaders.