Like you, I recently bought a potted,grafted Shenandoah 'tiny' plant and transpotted it into a bigger pot, where it has grown OK with 2 small branches developing full-sized healthy leaves. An identicle-looking tiny grafted KSU Atwood from the same seller that was packaged the same, growing in the same kind of nursery pot, repotted by me the same into the same kind of tall pot on the same day in the same soil mix with the same fertilizing and the same watering and the same Sunlight....never had one bud on the tiny scion grow out. It's rootstock sent out a couple shoots, but even these declined and died. I have used Miracle Grow, Super Thrive, and some granular fertilizer to nourish both. My conclusion is that the tiny root system is not reliable to support the tiny grafted scion. I have more confidence in clipping off the scion and regrafting it to a mature paw paw with a developed root system. I do not know what the patent restrictions dictate, but if I am going to invest $$ on a valued scion that is only being kept alive by an immature, very vulnerable rootstock, that is not a safe bet to make again. It would be a whole lot better taken care of if it was grafted onto a "Mango paw paw that has been in the ground for several years and is 8 or 9 feet tall". I wish that paw paw roots on tiny plants were as eager to grow and hardy as,.. say,...mulberries. Maybe that would be the best focus of additional paw paw research. Vigorous hardy rootstocks.

The 'why' is typically a combination of weather and photoperiod (day length). These are generally what most plants respond to when getting ready to flower and often fall conditions will mimic what the plant would normally experience earlier in the year, so it is "fooled" into thinking it is spring and time to produce flowers. Blooming out of season is rarely a cause for any concern and also rarely affects the normal bloom season for the coming year.

I think there are a few weeks to go before it freezes here! I, on the other hand, have been disappointed with how hot it has been for September in Colorado, because I just divided a bunch of perennials hoping cool weather was imminent so they'd have an easier time establishing. 80-degree weather is not great for plants stuck into the ground with hardly any roots. I think I lost some of the oriental poppies I took root cuttings from and some of the other plants are looking pretty sorry. Anyway, I'm in Colorado also, growing brugs indoors and out. Are yours in pots? If so, and if the "big freeze" comes and they are still blooming or have not yet bloomed, they will be perfectly happy to continue blooming in the warm house for a couple more weeks until finished. If you can set one in front of a sliding glass door, that's great. But even if you don't have the best light, they will continue blooming until the current crop runs its course, then they will return to a more vegetative growth or start going dormant. A full crop of brugmansia flowers in the house has a very intense scent that penetrate absolutely everything at night; its pretty intoxicating. I've put them in the garage before and they kept putting out new flowers in total pitch-black darkness for about 3 weeks. First, the leaves dropped. Then the newly-opening flowers became smaller and paler, until finally the remaining small buds dropped and the plants went dormant. It didn't seem to hurt them at all and they happily came out of dormancy in the spring.

I don't think I have ever been to a nursery where they know much at all about them or their care, except some do know that there are are hoyas and are aware of a couple of varieties. LOL There is one nursery near here that actually used to get in several different species at times, but they were only labeled Hoya plant and a few generic suggestions on care. They had compacta, lacunosa, kerrii, both kinds of variegated carnosas, pubicalyx Pink Silver, and carnosa Krinkle 8. When I would ask the ordering lady if & when they were getting them in, I would ask for a certain one and she didn't have a clue, so when I would see one, I went to her with the name and told her she should start labeling it that way. About a year later I was in there and sure enough she had them all labeled with the names I gave her. I was so happy I had done something to help hoyas and the people who like them. Then when I went back this year, the lady was gone, the only hoya I saw was one lowly looking carnosa Krimson Queen, and the label said, "Hoya Plant". LOL...it's hopeless. I do also find it puzzeling that such a lovely species that is easy to propagate and raise is not showing up in amongst all the pothos and other common plants all over the stores. Heck, you even see ORCHIDS everywhere now. But finding a variety of hoya hanging in any store or nursery is still as rare as finding gold while hiking the hills.