Verification builds:
1.2.0.7 Retail

Summary:
When pressing tab to complete a command, it sorts the choices incorrectly, ie not by the first letter typed. (Instead it sorts every command that contains that letter, alphabetically). This was not how tab to complete worked before 1.2.

Steps to Reproduce: (Just one example)

1. Type the following: /enchant @p u
2. Press tab

Observed Results:
The tab to complete chooses "aqua affinity" first, as it's first in the list of commands that include the letter U.

Expected Results:
It should only tab to complete words that begin with U (In this case, "Unbreaking")

Screenshots/Videos attached: Yes

Notes: