When you enter a command in the chat and use more than one space to seperate the argument an errors is shown but the command still executes. This behaves the same in singleplayer and on a server.

Example:

/execute     run   say     t    e     s     t

This seems to be caused client side because a Paper Sever logs the command with only one space into the console.

Sertonix issued server command: /execute run say t e s t