@a no longer works in actionbar text

Verification builds: 1.2 (464771)

Summary: @a @p etc no longer appear in titles, subtitles or action bar text.

Impact: Selector is displayed in text rather than player names.

Repro Steps:

1. Run command /title @a actionbar Great job @a ! You did it!

Observed Results:

@a appears in the text, rather than a comma-separated list of player names.

Expected Results:

The text should contain player names.

*Screenshots/Videos attached: * No
Notes: N/A