In negative X or Z locations, dismounting a minecart on a track next to a ledge, or on a 1 wide track can cause a player to dismount over an air block. This issue is similar to MC-36482, however the fix put in place making the dismount radius smaller doesn't fix the potential to harm players.

Example of the issue:
https://www.youtube.com/watch?v=hEWbUOhESBs
(Note, this was recorded in the previous snapshot, but I've since tested it on the most current)

Steps to reproduce:
Move to an X and/or Z position that is negative and make a 1 wide North-South and a 1 wide East-west rail suspended in the air. Leaving the minecart (Depending on your location) will leave you falling from the air to whatever is below.
Attached a screenshot to show exactly where the dismount locations are (The redstone blocks indicate where the player dismounts)

Finally:
In MC-36482 ElNounch explained the problem and the fix by flooring the values, and I've had someone make said changes to his vanilla minecraft, and the minecarts in -x and -z were no longer deadly.