filter_plugins cannot be used inside role defaults

Hi,

We recently migrated to Ansible v2.4 and having issues related to using our role-specific custom filter plugins in role defaults.

In previous version, this worked:

- myrole
    - defaults
    - filter_plugins
    - tasks

We could use filter plugins defined in this role in the defaults variables but this does not work any more.

It fails with error "template error while templating string: no filter named 'some_filter'." But we can use those filters in tasks.

Is this something expected? We are trying to make the playbook work again, with minimum modification. Any suggestions?

Thanks in advance.