Examples:

Tab-completing "/gamemode " (2 spaces after "gamemode") will return the list of players
Tab-completing "/setblock 20 20 20 20" (2 spaces after "setblock") will return the options for oldBlockHandling
Tab-completing "{{/setblock }}" (4 spaces after "setblock") will return the list of blocks

This is an issue because commands will still work if additional spaces are included: "/setblock 325 5 -719 20 0 destroy" works the same as "/setblock 325 5 -719 20 0 destroy"