Wrong encoding after activating resource filtering

I am developing a maven based web project. In my web module I am using different language specific resource bundles (german, spain, ....). All my sources are based on UTF-8 and erverything works fine. Now it was necessary to acitvate maven resouce filtering to replace some configurations depending on different maven profiles.

my pom.xml:

.....
 <project xmlns="http://maven.apache.org/POM/4.0.0"   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
.....

 <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 </properties>    
 <build>
 <resources>
    <resource>
    <directory>src/main/resources</directory>
        <filtering>true</filtering>             
    </resource>      
 </resources>
 ....

From this moment my war file contains resource bundles with wrong encoding. For example German umlauts are no longer displayed in my web application correctly. When I disable the resource filtering everything is well again.

The only solution I found was to set the property project.build.sourceEncoding to 'ISO-8859-1'

<properties>
  <project.build.sourceEncoding>ISO-8859-1</project.build.sourceEncoding>
</properties>

But I can not understand why this is necessary? All my sources are UTF-8 and also my application is based on UTF-8? What will happen if I need to add a resource bundle with - for example Japanese characters?

I am developing on linux using Eclipse 4.2 and Maven 3