Cedric Lippke

Also the space between the enchantment name and the level of the enchanment is missing.

Confirmed for 18w01a

Error:
The target does not have the specified slot

for command:
/replaceitem entity @e[type=chest_minecart,distance=..5] container.0 minecraft:dirt

one way to achieve the same:
/data merge entity @e[type=chest_minecart,limit=1,distance=..5] {Items:[{ Slot:0b,id:"minecraft:dirt",Count:1b}]}

The clear and give command don't work in the 1.11 snapshots, too!