I have added some support for the Digest subscription type for an application we are using. But action_edit and action_post do not properly handle this subscription type.
Code needs to be added to the switch statement starting at line 275 in action_edit and line 229 in action_post.
I'm not sure what you are asking for. There is no support for any type of digests in core.
So I would see this as a feature request, right?
I am not sure it is a feature request, or a bug.
PHORUM_SUBSCRIPTION_DIGEST is defined in the core. So if one of my mods creates/changes the subscription type in a post, then I would expect that the core should at least not generate an error and/or lose the setting.