Pressing TAB no longer cycle through possible command values

The bug

In 1.12.2 pressing TAB used to cycle through the possible command values. Starting in 17w48a this is not the case anymore.

How to reproduce

1. Type the following in chat

   /ga
   

2. Press TAB to complete it to "/gamemode"
3. Press TAB again to cycle to "/gamerule"
   → It will does not change