diacetyl in bottles after keg?? -beer gun

Not sure where to ask this question but here goes.

I normally PM but did an extract/steep amber ale since I wanted to get a batch done quick.

All went well. 2 weeks primary 2 weeks secondary, keg and let sit about a week on 12psi with a sample here and there. When the fierce hop bite subsided I thought it tasted pretty good and called it done. Using my brand new beer gun I bottled a six pack and took to the in-laws for thanksgiving. It went over well and one brother-in-law who home-brews too drank 3 to himself so I knew it was good. I bottled another six pack for a future card game at a friends house, since I knew the keg wouldn't last. And it didn't

2 weeks later (this last weekend) at the card game. My bottled beer had a total butterscotch taste and smell. (overwhelming IMO) My buddies didn't know any better but I was royally dissapointed.

My question is why the huge difference in taste? If my beer had alot of diacetyl wouldn't I have noticed it earlier? I used dry yeast and temps were good. Did I not clean the beer gun well enough and introduce an infection?

The answer is, that it really depends. Maybe this will help shed some light on the subject for you.

hmmm after reading that site I wonder if this could be my culprit?

. . .when diacetyl appears spontaneously in a beer that seemed to have normal flavors. Strong evidence indicates that this can occur when marginally dysfunctional yeast have been used in the main fermentation -- they tend not to metabolize all the acetolactic acid in the wort. The acetolactic acid spills over into the finished beer and later is oxidized to diacetyl.

Click to expand...

How do you know if you used "marginally dysfunctional yeast". It was one pack of dry yeast. Safale if I remember right. And my OG was ~1.048-1.044

I had the same problem after kegging. After 3 weeks the brew in question turned out to be the best nut brown I have ever made. My advise would be just to get it a little more time for the flavors to mellow