On page 22 of the book it clearly states
" Players immediately advance to the next stage of a quest as soon as they place a number of progress tokens equal to or greater than the number of quest points the current quest card has. "
and
" the round sequence is not interrupted. "
nevertheless the last week I have found myself in a sort of silly situation
While playing The Lonely Mountain from the "The Hobbit: On the Doorstep". We were on quest 2B with Smaug the Golden in the staging area. During the quest phase, we revealed Pretending to Sleep , which added the 6th progress token on Smaug the Golden . As per the rules, we advanced to stage 4A , which removes Smaug the Golden from the game and adds Smaug the Magnificent to the staging area. Since the rules state that the round sequence does not interrupt when you advance the quest, we finished resolving the quest phase. Since Smaug the Magnificent, in our case, contributed far less threat (only 6) than Smaug the Golden ( 1 threat for each character committed to the quest), we had enough progress on quest 4B as to complete it; removing Smaug the Magnificent, adding back Samug the Golden and advancing back again to quest 2B. That felt very silly.
It is how it is intended to be played?