Hi,
I have experienced with problem before. I live in Houston ,TX, like you said my flowers were malformed and the leaves looked a wee bit strange. I found no bugs/pests but I went ahead and just sprayed with a regular insectide spray (I am sorry I can't recall the name) and fertilzed my planst every 20 days with all purpose liquid fertilizer and watered them more thoroughly every day and this showering of attention seemed to help by Hib reciver pretty well in 45 days time.
Good luck..I am sorry that I do not have a scientific explanation to your problem but this is what I did emprically which seemed to help!

I'm not in TX but imagine Hibiscus to be the same all over, been raising them outside in the ground 29 years now, and can tell you, they DO NOT LIKE WET FEET, they do not like bug spray of any kind, but much prefer a systemic for flowering plants, and I feed mine with granular food for acid loving plants.Frost wll set them back and a freeze can kill them, I do not plant on the north side of my house, that is for evergreens and I'm in SW FL.