Minecart deflects to side when broken by cactus or lava

Steps provided in comment, analysis in the subsequent comment.

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I have several automatic minecart stations.  Upon arrival the minecart strikes a cactus and is sucked into a hopper beneath the rail.  At least that's how it used to work.  The minecart is now deflecting in a seemingly random direction (right or left) and missing the hopper.