Common prefixes are no longer tab-completed

The bug

In 1.12.2, common prefixes were automatically tab-completed. This allowed people to easily narrow down the result set. As of 17w50a, this is no longer the case.

How to reproduce

1. Type /scoreboard objectives add name m
2. Hit tab

You will be given a huge list of tab-completion suggestions. Finding the one you need will be no faster than typing it. However, 1.12.2 Would first tab-complete to /scoreboard objectives add name minecraft. - from there, you could keep on specifying what you need, for example by adding a b at the end and hitting tab again, which would give you /scoreboard objectives add name minecraft.broken: and so on.