In a multi-module build (reactor build), the dependency:analyze(-only) goals output some odd looking text which is missed by the parser when matching errors:

...
[INFO] [dependency:analyze-only

]
[WARNING] Unused declared dependencies found:
[WARNING] active project artifact:
artifact = active project artifact:
artifact = active project artifact:
artifact = active project artifact:
artifact = active project artifact:
artifact = active project artifact:
artifact = com.example:sampleLib:jar:1.0-SNAPSHOT:compile;
project: MavenProject: com.example:sampleLib:jar:1.0-SNAPSHOT @ /home/jpringle/code/lib/pom.xml;
project: MavenProject: com.example:sampleLib:jar:1.0-SNAPSHOT @ /home/jpringle/code/lib/pom.xml;
project: MavenProject: com.example:sampleLib:jar:1.0-SNAPSHOT @ /home/jpringle/code/lib/pom.xml
[WARNING] junit:junit:jar:4.8.1:test
...

Note this output is only triggered under some invocation paths:
1) when dependency:analyze-only is wired into the multi-module build within the pom and the build is invoked with 'mvn clean install'.
2) invocation from the command line where compilation is triggered by something other than the dependency plugin:
mvn clean compile dependency:analyze-only
mvn clean test dependency:analyze-only
mvn clean compile dependency:analyze
mvn clean test dependency:analyze

Other paths work as expected:
mvn clean dependency:analyze

...

[INFO] [dependency:analyze]
[WARNING] Unused declared dependencies found:
[WARNING] com.example:sampleLib:jar:1.0-SNAPSHOT:compile
[WARNING] junit:junit:jar:4.8.1:test
...