Scoreboard objective criteria tab-completion does not account for namespaces being optional. Leaving out one or two of the namespaces gives a live error message ("Unknown criteria name") until the argument is completed manually. To reproduce, first type in

/scoreboard objectives add test

and then type out any of the following examples for the criteria argument:

• broken:stone
• minecraft.broken:stone
• broken:minecraft.stone
• .broken:stone
• broken:.stone
• .broken:.stone
• minecraft.broken:.stone
• .broken:minecraft.stone

Observe the tab-suggestions disappear and a live error message appear instead. Note that all of the examples given are valid and working criteria.