The Bug
When summoning a minecart and then it gets pushed by another minecart it can stay visually tilted in the air.

Command

/summon minecraft:chest_minecart ~5 ~ ~ {NoGravity:1b,Invulnerable:1b,CustomDisplayTile:1b,DisplayOffset:16,Rotation:[180F,50F],OnGround:0b,DisplayState:{Name:"minecraft:cobblestone"}}

Replicate

• Summon a minecart with the command above
• Move a bit forward
• Summon again (might take a few tries but the minecarts need to be summoned close enough that they push each other a bit)
  Notice that the second minecart summoned is tilted and won't revert back