We were impacted by this update too. One of our teams doesn't use resolution/closure categories either and having a category level set down to the maximum levels in the service configuration provided a solution.
Hornbill insist that something has been addressed so that things work "correctly" in relation to this setting. However, if you refresh you browser the mandatory message disappears. That new behaviour Vs a previously logical (and reliable) approach to the situation makes the "fix" hard to stomach. It's as if someone saw the description of the application setting and took offence. One might think it was easier to caveat the description of the setting. The motivation for this "fix" is a little baffling.
The lack of an alternative to support the preferences of different business areas on the platform, or any commitment to fill the gap in capability which has been created, adds more frustration to the situation. It's not often I throw my toys out of the pram, but this one has created back-lash for us too.... and on a side note, I'm still waiting for an update on my escalation in relation to this.
In my opinion, setting the resolution category before the ticket is resolved is not the right approach. Secondly, what are we meant to set it as, just a generic one? I'll have to review my category-related reports to exclude such a value as its essentially acting as a placeholder for those teams where the category isn't of any use.
Dan