20 Month Old Suddenly Throwing Tantrums for bed!!?

My son is 20 months and has always been a fabulous sleeper. We have a little betime routines that involves 2 books, a few songs while we snuggle and then "night nights" with his crib soother and glow bug to play him music until he falls asleep. At 10 months we went through the typical separation issues and had to let him cry it out a few nights...but other than that and a few nights sick or teething...he is a FABULOUS sleeper. The past 3 nights however--for nap and bedtime he has thrown a tantrum the minute I tell him "night nights." We still go through bedtime routines and he is great for that. The second I put him in the crib he flails and wails and puts up a fight. My rule is--I pick him up once and give him one more kiss and tell him No honey it's night nights. Then I lay him back down and leave the room with him still crying. He rarely cries over 2 minutes. I'm watching him on the monitor now and he is currently playing away with his glow bug, hugging him and kissing him and singing to his soother music, with only a few whines here and there, so I know nothing has been WRONG these past few nights. My question is this--is this a typical stage? I've noticed in the past week or so he has REALLY skyrocketed in the independence department. Eg. trying to dress himself, telling me when he has a 'poo,' bringing me his shoes and asking me to go "A-side?" Are these tantrums just a phase as he begins to understand he is his own person? Anecdotes from other mommas would sure put me at ease. I know this isn't a horrible issue. But I hate putting my little one to bed with tears when our bedtime routine was once such a precious and special time.