II think you have figured it out. The tuberhybrida are not really bred for hot summers, I think they are at their best in August, at least in my climate, because the nights are much cooler than in July and the daylight is less direct although the temps are still high. Five of the six species which make up these plants are found in the Andes, I believe at about 8,000 ft, so cool growing conditions are really more natural to them. Professional nurseries have the knack of breaking tuber dormancy early and when you may buy in April or May they are in full b loom, but they still have to learn to deal with outdoor conditions outside greenhouses. I wish Andy from Golden West was still on this site, he could explain things better than I.

my understanding is that they like cooler nites (55-60f?) and warm days (75F?). so I kinda hope that in the next 6 weeks they will all perk up (it's been unseasonably cool here, as in many other places).
what I don't get is why on the same plant one stalk is producing well formed flowers, while the 2nd stalk does not.
so it's not some special nutes? AV fert has micros and is acidic, so I figured it should be good. may be I should just feed it hi-phosphate 8-14-9 exclusively for better blooms?

I dunno. YOu know the old saying, horticulture is not an exact science. . . The days are getting shorter now and that will trigger dormancy by September, although they often look good thru September.

Are these male vs. female flowers? That still confuses me...

these are male, the female flower has a kind of triangular shaped base. there's normally 1 male and 2 female on one stem.

Ooooh, I see that. Great pic, thanks! Man, that's pretty! So, you're comparing 2 different male flowers originally? And the top pic is the expected appearance? I'm not sure I would notice, unless someone else did and pointed it out. I just saw pretty flowers until like the 3rd time.

In general, I'm fascinated by the things going on with Begonias I hadn't even noticed or heard of yet, until "you guys" say something.

LOL, I know pics are more fun then reading...
and i am not a specialist at all, just a casual grower, but i like to grow GOOD! if i can :).
i get full double flowers like on top pic on one plant occasionally and then the rest on the SAME plant like the bottom='semi-double'. and i have 2 plants of the same type. and on the 2nd plant it's ALL semi-doubles (like the bottom).
so i can't figure out why it refuses to produce ALL doubles?!
i mean, it's not diff growing conditions, these flowers are all on the same plant together!
i've got to the bottom of it, i think: they need stronger bloom ferts then 8-14-9 i'm giving. i use to have orchid 19-31-...smth and then my non-stops were all good.
now i read too many posts saying NOT to feed them strong ferts..and like a fool i'm trying to comply...
i'm going back to mighty orchid stuff!
i love the color on my picotees, if only they were fully formed it would be REALLY NICE!

here's proof of orchid 1-2-1 ratio feed a few years back. also non-stops, but diff kind.
what I find disappointing is that 'the real begonia specialists' have nothing to say on the matter. in the begonia forum.
I

just for the record: after 2 weeks of low 60f/75-77f my begonias are producing much better semi-double blooms. they are smaller, from secondary growth, but nice. i also started giving them double the dosage of AV fert of 8-14-9. may be that's helping too.

That's cool, but I thought they were stunning in every pic you showed! All beautiful, IMVHO! Kudos to you for being so observant.

Is that a Euphorbia with it in the past pic (which blows me away, BTW) - the little white flutter flowers?

yep, euphorbia 'silver fog' - it looked very good into fall. it's a great filler with petunias/begonias.