Currently, the Beaker model files use the SQL Alchemy "backrefs" directive. This confuses pylint, so we have the attribute checking errors in pylint disabled.
Those disabled checks likely would have caught bug 1124756 during continuous integration testing, rather than letting it escape as a regression in 0.17.
The back_populates directive records both sides of the link explicitly, and should allow the relevant pylint checks to be enabled, eliminating the chance of future bugs of that type making it through continuous integration.
This patch eliminates all backrefs:
but unfortunately it turns out that is nowhere near enough to fix all pylint attribute checking errors. So it will need more work before we can turn those on.
Beaker 20.0 has been released.