Messages shown in the action bar aren't correctly positioned when there're bold characters followed by normal characters

Steps to reproduce:
1) Create a resource pack
2) Change "Press (key) to dismount" to something like "§lTesting bugs §f- This bug can be reproduced in vanilla minecraft "
3) Get on a horse, and the action bar message will be lefty

This affects both resource packs and messages sent by custom servers, I'm re-posting this issue because MC-77414 was closed and didn't get reopened after a user provided a way to reproduce this bug in vanilla.

I also made this resource pack for people that don't know how to create a custom language file, enable it and then select the language "Test":
http://www.mediafire.com/download/s7dmq1b2c0uw2d1/Test.zip