I don't remember reading anything to indicate that Panda is an on-off switch. In fact, I recall just the opposite. Panda demotions hit websites with a highly varied impact - losses in the single percentage points up to major and devastating declines.
Given that kind of variation at the onset, I am not at all surprised that sites report - and they do - a wide variation in how recovery happens. Panda is a very complex beast, affecting even different pages and keywords differently on any given website.