When using Ivy to resolve dependency in my project with this line:

<dependency org="org.slf4j" name="slf4j-log4j12" rev="1.7.5" />

slf4j-api-1.7.5.jar and log4j-1.2.17.jar aren't resolve. I've open the
ivy-1.7.5.xml file in Ivy cache, I've got this :

<dependency org="org.slf4j" name="working@xxxxxxxx" rev="1.7.5" force="true"
conf="compile->compile(*),master(*);runtime->runtime(*)"/>
<dependency org="log4j" name="log4j" rev="working@xxxxxxxx" force="true"
conf="compile->compile(*),master(*);runtime->runtime(*)"/>

At working@xxxxxxxx, the xxxxxxxx are my machine host name. When I edit the
file with dependency found on Maven central like this:

<dependency org="org.slf4j" name="slf4j-api" rev="1.7.5" force="true"
conf="compile->compile(*),master(*);runtime->runtime(*)"/>
<dependency org="log4j" name="log4j" rev="1.2.17" force="true"
conf="compile->compile(*),master(*);runtime->runtime(*)"/>

It works as soon as I trigger a new resolve with Ivy. So I looked in the pom
file on Maven Central and I found that the required version attribute in
dependencies are missing. Here the extract of the pom file currently on Maven
Central:

<dependencies>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
    </dependency>
</dependencies>

and here is what it should be:

<dependencies>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>1.7.5</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.17</version>
    </dependency>
</dependencies>

This problem appears on every versions of slf4j-log4j12