I'm on Nar Shaddaa doing heroics and I noticed this as well, but not odd levels but at each level gain, if that helps the devs about this issue.
Edit new info: The health drop seems to occur while in combat. Out of combat, no drop but goes to full like normal.
New update: was in story instance, out of combat, leveled after the dialogue, dropped to low health. Combat appears to not be it.