I am sure that the APA at one time had and or commissioned such research PRIOR to blindly embracing all things homosexual; however, I myself can not recall anything...
Scripter might be able to reference something though.
I will put looking for any studies on this on my to do list and ping you should I find anything.
Unforunately I don't know of any studies on the subject. I've seen studies that hit on the subject but none specifically on the issue of molestation. While molestation is certainly one avenue into homosexuality, there are many factors involved, and of course environment remains the key factor.