success! see below for more info

race condition between flask's debugger and the global session in
sessionmaker, but this can get gotten around by not using flask's
debugger

However, this isn't ideal for development, and this can be gotten around
with scoped sessions:
http://docs.sqlalchemy.org/en/rel_0_9/orm/session.html?highlight=scoped_session

I will try this next before moving onto flask-sqlalchemy