I don't know why my last bug was closed immediately. The response was not helpful so I am opening a new bug to address the tab completion setting in spigot.yml not behaving as expected.

My old bug:

https://hub.spigotmc.org/jira/browse/SPIGOT-6338

My spigot.yml is using the default setting tab-complete: 0 but my TabCompleter is only called after the first character of the argument is typed.

According to the documentation:

0 will tab-complete all commands
-1 will disable tab completely
1 will mean you have to type the first letter
2 will mean you have to type the second letter... etc...