Yes, I do believe you have accurately described the behaviour we are seeing, Baily18. However, that we can understand why it is occurring does not necessarily mean it isn't a bug.
I would have thought that Parallel Universe should produce a creature that behaves exactly as the creature that it copies. That would mean that it should not get the life of the original, which is already adjusted for Scarabs previously in play, and then get an additional adjustment for those very same Scarabs being in play.
It's certainly behaviour odd enough to question whether it is intentional.