type /gam and press tab -> cycles between gamerule and gamemode
type /gam and press space -> autocompletes current selection and adds a space
type /gam and press enter -> autocompletes current selection and doesn't add a space
type /gamem and press tab -> autocompletes gamemode and doesn't add a space
type /gamem and press space -> doesn't autocomplete and adds a space
type /gamem and press enter -> doesn't autocomplete and executes command

Basic rules that should make this consistent:

• Enter should never autocomplete anything and always run the command
• Behavior when having one option should be the same as having multiple options
• Auto-completing a full argument should always add a space