[logback-user] Still getting log4j messages

We're using slf4j and logback in our app. We've got an app that depends on a library that depends on log4j (freemarker). When we invoke the library, we get: log4j:WARN No appenders could be found for logger (freemarker.runtime). This is strange, because log4j isn't on the classpath. We *do* have log4j-over-slf4j on the classpath, and we do have "freemarker.runtime" defined in logback.xml. Logback.xml is getting properly read and used by other parts of the application. Any suggestions on why the Freemarker library isn't properly using log4j-over-slf4j? Where should I look?