What steps will reproduce the problem?
1. Cast any form of Rejuvenation that has a duration longer than 12 seconds (its intended base duration in 3.2 and before), this includes rank 15 Rejuvenation on live servers(has a bugged 15 second duration), any rank of Rejuvenation on the PTR(an intended 15 second duration), any rank of Rejuvenation on live or the PTR with the talent Nature's Splendor(increases Rejuvenation's duration by 3 seconds)
2. Wait for the sparkling HoT bar to tick down for 12 seconds.
3. Observe the bar disappear!

What is the expected output? What do you see instead?
The HoT sparkles are expected to last the full duration of the Rejuvenation spell, but at the moment only last 12 seconds regardless of talents, changes in base duration of the spell, or other considerations.  

What version of the product are you using?
Error occurs both on the 3.0.6 Release Proper, and the new 344 alpha.  

Do you have an error log of what happened?
I do not.  Sorry!

Please provide any additional information below.
I imagine that this problem is only going to get worse in the 3.3 patch, where the duration of the spell can be changed by the player's spell haste value if the appropriate glyph is applied.