A few months ago I posted about what appears to be a bug with Conditional Formatting in MM 2018 when tags are used as a trigger. Unfortunately this problem does not appear to have resolved in MM 2019 (including the latest service pack) despite the revamping of Conditional Formatting as SmartRules, and I've discovered that it also affects Resources.
To reiterate, if a rule is set so that a tag or resource is the trigger and "Is Exactly" the condition, then in my view the rule should apply only to topics which have only that tag or resource present. However, it appears the rule can still be triggered if there are multiple tags, provided the target tag is present among them. The same thing happens if a resource is used for the trigger instead of a tag.
In other words, "Is Exactly" and "Contains" appear to work the same way as triggers when applied to tags and resources, which is illogical and is also a serious limitation on the usefulness of SmartRules. What should happen in relation to tags for example is that "Contains" should trigger the application of the rule if the target tag is present among multiple tags, but "Is Exactly" should be applied only if the target tag is the only one present. The same should apply to similar rules used with resources.