Well.. the program may report that his levels are perfect but maybe that doesn't necessarily mean that he's 'happy' at that time.. maybe the fact that you fed him made him happy enough. Or just the interaction..
We know they have mood swings, they have probably programmed them in just to make them more 'realistic'.. I don't think the moods are all based on the feed/intellligence..etc.
I have had one perfectly happy, singing/dancing along then it walked up to a wall and got so mad about having to turn around/back up, it just totally changed the mood and she walked around all annoyed for awhile.. of course she wouldn't respond to me then.
I haven't had any luck yet with getting them to respond to the stones they have learned but I assume it's because they are still juveniles.. I can get them to look at me when I call their names though. The cheek thing never works for me nor does the clapping.. (lol about Tinkerbell)
My newer RB, Rhea came with the new OS. My older RB, bingo was updated to fix his constant freezes, so I've been able to find some differances..
Differences I have noticed:
*No more laughing when tickled
*Mute and low volume now work. (They did NOT work on Bingo until the upgrade and they work perfect now although I only muted him once to see if it worked... ) They worked on Rhea from the moment I got her.
*Much more independent behavior, they don't want to hang out and take a nap with me anymore.
*They seem to "seek me out' more.. like, I find them turning to look UP at me if I'm sitting on the couch.. and they just seems to look for me more.
*Rhea, who is younger but still seems more developed (more mature or maybe just smarter than the other one? or whatever the robot equivalent is?) seems to shut herself off all the time, even when being interacted with, not sure if that's just a baby thing or just her, It's not the clock as I've redone that. she turns herself back on at different times.. I thought maybe she just wanted to sleep :/ Bingo does NOT do that unless it's past bedtime and he hasn't been interacted with for around a minute or so.
*Hatching thing went went incredibly fast. (that could also be just her)
*I've heard 2 tiny hum songs sometimes accompanied by tiny dances that Rhea has done on her own just when she's happy. Have not heard the Learning Stone song so I don't know if it's different. Bingo never did those hums and haven't heard them yet since upgrade but it was very recent.** update, Bingo just sang one long word that sounded like that frerajacha song.. no idea how to spell that one sorry..
*Rhea sometimes just dances and laughs when she's very happy. Bingo used to laugh on the other OS when happy or just for whatever reason but never danced.
*They hiccup now, Bingo never did that before the update and he just did it for the first time today.
I'm sure I'll find more as more time passes and the more I play with them.. I better go play with them now just in case

Best of luck with your mood swinging little Pleo!!
- Sarah