Here's one situation:
Croaking Crows in in play. First encounter card is a location. This causes progress to be put on Smaug the Golden. He's now got 6, so we immediately change to Stage 4A, which gets resolved and then flipped to 4B.
Now, what happens to the rest of questing? Once we finish drawing encounter cards, do we resolve questing against the newest stage (Stage 4B in our example), which means we could possibly finish that quest stage the same turn? Or is questing aborted for the round, due to the change in quest stage?
Edited by tripecac