@FacesConverter annotation not working with tomcat7-maven-plugin

Question

I have an application packaged as WAR file, which runs perfectly fine in a standalone tomcat (7.0.67) but it does not work properly with the tomcat7-maven-plugin using mvn tomcat7:run .

The problem is that there are custom converters defined, e.g.:

import javax.faces.convert.Converter;
import javax.faces.convert.FacesConverter;

@FacesConverter( "custom" )
public class CustomConverter implements Converter, Serializable {
  ...
}

which seem not to be registered, because I get the following error and the application does not load properly:

Dec 15, 2015 10:27:01 AM com.sun.faces.application.ApplicationImpl createConverter
SEVERE: JSF1006: Cannot instantiate converter of type custom

However, if I register the same converter in the faces-config.xml, all works fine:

<converter>
    <converter-id>custom</converter-id>
    <converter-class>com.package.CustomConverter</converter-class>
</converter>

So the problem seems to be with the different libraries in the standalone tomcat and the tomcat7-maven-plugin. But I could not figure out what exactly it is. Please, let me know if you have any suggestions, thanks.

dependencies from the pom.xml and the tomcat7-maven-plugin:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.tomcat.maven</groupId>
            <artifactId>tomcat7-maven-plugin</artifactId>
            <version>2.2</version>
            <configuration>
                <port>8080</port>
                <path>/</path>
            </configuration>
        </plugin>
    </plugins>
</build>
<dependencies>
    <dependency>
        <groupId>com.sun.faces</groupId>
        <artifactId>jsf-api</artifactId>
        <version>2.1.20</version>
    </dependency>
    <dependency>
        <groupId>com.sun.faces</groupId>
        <artifactId>jsf-impl</artifactId>
        <version>2.1.20</version>
    </dependency>
    <dependency>
        <groupId>javax.el</groupId>
        <artifactId>el-api</artifactId>
        <version>2.2</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.jboss.el</groupId>
        <artifactId>jboss-el</artifactId>
        <version>2.0.1.GA</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
        <version>2.5</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.security</groupId>
        <artifactId>spring-security-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.primefaces</groupId>
        <artifactId>primefaces</artifactId>
        <version>3.5</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-support</artifactId>
    </dependency>
    <dependency>
        <groupId>org.primefaces.extensions</groupId>
        <artifactId>primefaces-extensions</artifactId>
        <version>0.6.3</version>
    </dependency>
</dependencies>

subset of the web.xml:

<context-param>
    <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
    <param-value>server</param-value>
</context-param>

<context-param>
    <param-name>javax.faces.PROJECT_STAGE</param-name>
    <param-value>Production</param-value>       
</context-param>

<context-param>
<param-name>javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL</param-name>
    <param-value>true</param-value>
</context-param>

<context-param>
    <param-name>javax.faces.VALIDATE_EMPTY_FIELDS</param-name>
    <param-value>true</param-value>
</context-param>

<context-param>
    <param-name>javax.faces.FACELETS_SKIP_COMMENTS</param-name>
    <param-value>true</param-value>
</context-param>

<context-param>
    <param-name>javax.faces.DEFAULT_SUFFIX</param-name>
    <param-value>.xhtml</param-value>
</context-param>

<context-param>
    <param-name>com.sun.faces.enableMissingResourceLibraryDetection</param-name>
    <param-value>true</param-value>
</context-param>

<context-param>
    <param-name>com.sun.faces.expressionFactory</param-name>
    <param-value>org.jboss.el.ExpressionFactoryImpl</param-value>
</context-param>