Diazo: css: if-content and css: if-not-content are the same

I use Diazo on the Plone website (4.2), and in the rules.xml file I have something like this (this is simplified, but I also tested this simplified version).

    <rules css:if-not-content=".add-post-link">
        <replace css:content="#content" css:theme="#document-content" />
    </rules>

    <rules css:if-content=".add-post-link">
        <drop css:content=".documentFirstHeading" />
    </rules>

The problem is that both the "replace" and "drop" directives are applied, which means that both conditions are met: "css: if-content" and "css: if-not-content", although they complement each other , i.e. one and only one of them must be true at the same time. (By the way, if I switch the order of the two "rules" directives, the result will be the same)

Does anyone understand this behavior? Is this a mistake or am I missing something?