A speaker may omit emphasis where denial appears to call for it, or emphasize a fact for a listener who does not verbally deny it. Such a shift can be analyzed as departure from the apparent situational expectation, but only where the context supports a rhetorical purpose.
For instance, a person may acknowledge an obligation yet consistently act as though it carries no force. A strong assertion about the responsibility attached to promises can treat practical indifference as akin to denial. This is not merely a grammatical effect of inna.
An explanation should identify the conduct, setting, or surrounding discourse that motivates the deviation. Inventing a psychological story to justify every unusual expression would make the analysis unfalsifiable.