PC
Broadband
Time Warner
Always
Everyone
Everywhere
Any Class
Any Skill
Steps:
1. Log in, then wait (some users report that it gets progressively worse as they're logged in)
2. Use ability. Ability cooldown will not display correct time

For reference, I've had times where Jarring Strike II never shows a CD timer at all due to this. An LS mate said her timers were off by 15 seconds at one point.