Originally posted by GodsPetMonkey: I'd say that it almost certainly is. I suspect astrotracer will only change in B, and a user mode based on Bulb won't count.
On my K5-IIs, I always do astro with a user mode. It invokes Astrotracer and is, in fact, based on Bulb. I have occasional problems with AT but it usually seems to happen when I navigate away from the capture mode (e.g., to review frames I've gotten so far) and the focal-length setting wanders to some other value. For some reason my camera really, really likes to believe it has a 50mm hung on the front, even when it has a 14.