For the most part, I have to side with Ian. Then again, it's possible that a difference in temperature (warmer) can make even a laminate more responsive. My first guitar was a Yamaha that was made of laminates. If I picked it up after it sat around for a long time, it usually took a little while before the sound would "open up" some. I always referred to that as "crankiness from neglect."
Perhaps you're playing your uke a little more lately? Practice makes perfect when tuning up.
Speaking of, another factor Ian missed was that of strings being in or out of tune. My KoAloha Soprano is very tempermental if the strings are even a little out of tune. Over the first year of my getting serious with playing uke, I discovered that fretting the strings too hard would throw the strings off pitch--enough that I could hear a difference. Also, the action of the strings (string height above the fretboard) affected pitch, further up the neck (towards the sound hole) I went. Somewhere in the middle of this mix of factors, I found that how I tuned my uke would affect the sound when I played it. Prior to my finally getting a good clip-on digital tuner, I really had to dink with things before I found that sweet-spot with the tuning. That's a lot of work--especially if you're fretting the strings and popping harmonics and struggling with friction tuners.
Pretty much nowadays my KoAloha sounds great, now that I can get all the strings properly tuned. The sound does "bloom."
--Dave E.