In Org mode's info, I could not find any requirement that the property
drawer must be the first thing in the entry.  However, this is the case in
recent versions of Org.  Things work OK in the following version:
Org-mode version 8.2.10 (8.2.10-42-g2e1bc4-elpa @
/home/jorge/.emacs.d/elpa/org-20150727/)
but things fail in recent versions, particularly 2015-08-24 (which I
uninstalled because it kept pestering me about many supposed "malformed
drawer"s because of this bug).

If have created a small file that reproduces this bug, and attached it to
this email.  In this file,
with old Org and point at the beginning of the drawer,
org-get-property-block returns
(33 . 52).
New Org returns nil.

This is Emacs 24.5 compiled from sources in Ubuntu 15.04.