When a minecart falls onto a cactus, it breaks before coming close to touching it.

See below comparisons, sand 1 tick before breaking (the next movement step would place it inside the cactus), the player right above the cactus (the cactus isn't the issue), the chicken 1 tick before damage, and then finally the video and the minecart 1 tick before breaking.

The chicken, despite having a much slower falling speed, was able to respond to damage later than the cart, which, pictured, reacted to the cactus 2 ticks earlier than the others and from farther away.

The only other thing that does this is boats, which seem to have the issue even sooner, regardless of if their next position would place them outside the damaging area.

Entities with identical falling speeds react accordingly, yet minecarts and boats always respond sooner than they should be.