The second reason is associated to the changes brought by Cataclysm: much larger health pools and "smaller" heals. In Wrath, tank HP were oscillating like mad, here I'm testing tracking on a DPS (much smaller damage intake) and huge health pools which are not meant to be healed in a single spell. As a result, the inconsistencies coming from the timing issues (sequence errors resulting in heals arriving before the damage is inflicted) are a lot less visible.
I had to do some internal changes, so that on the health display zooming in provides better resolution for picking and displaying events (there are tons of small heals going on...), and I did some other minor quality of life improvements. As soon as I can get a windows compiler running, I'll create the "MoP release" and put it up for download. If you're curious: health tracking in the final Elegon phase looks like this:
(in case you wonder: the final red line is Elegon one-shotting me with his final attack)