Well, Im new, so can't give you an experienced point of view, but your question reminded me of something I dicovered - maybe it will help you.
I discovered when trying to tackle housework (reluctantly) that if i flit from job to job, it gets done quicker and I don't feel bored on the one task. In the end, its all done and I haven't felt it so much of a chore.
Anyway, maybe doing a few projects at once works good for you. I say, go with what works. Its probably your way of not going stale on the one job. It probably keeps your brain ticking and your interest high, even if you aren't aware of it.
Previously, I could never understand how one person could have more than one book they were reading on the go - until recently I unintenionally had 3 on the go - and I actually loved it. Going from one to the other was quite exciting. Maybe its the same for writing in your case?
