Linda: Are you still at your old e-mail address? I have some information for you from the archives in Graz.
The most important information is that Franz Johann Poschenreiter was indeed born in Graz, parish Mariahilf, on June 17, 1882, together with a twin sister who received the name Aloisia Anna. The parents were Johann Poschenreiter who hailed from Persenbeug in Lower Austria, and Aloisia nee Pittermann who hailed from Stegersbach, then Hungary (today Burgenland). The parents had married in Graz. However, they must later have divorced.
I have some more information which I will be happy to convey to you after confirming your e-mail address and finding the time for transcribing my notes.