Ivy converts pom.xml-Package-Tag into ivy.xml-Extension - ivy

Question

Problem
When using Jenkins Shared Libraries I try to #Grab('com.atlassian.jira:jira-rest-java-client-core:4.0.0'). This miserably fails while ivy tries to fetch dependencies:
General error during conversion: Error grabbing Grapes -- [download failed: com.atlassian.sal#sal-api;3.0.3!sal-api.atlassian-plugin, download failed: com.atlassian.httpclient#atlassian-httpclient-plugin;0.23.0!atlassian-httpclient-plugin.atlassian-plugin]
As far as I understand, this happens by the following reason:
Ivy downloads the pom.xml files for the dependencies, converts them into ivy files and downloads the corresponding artifacts. These dependencies state a <packaging>atlassian-plugin</packaging> in their pom.xml, which is converted into <artifact name="atlassian-httpclient-plugin" type="atlassian-plugin" ext="atlassian-plugin" conf="master"/>. Ivy tries to download *.atlassian-plugin files now instead of *.jar.
Is this a bug in ivy, that should be reported? Or is atlassian missusing the packageing-Tag?
Minimal example for reproduction
I can reproduce the problem independently from jenkins using ant/ivy locally with the following files.
[ivy:retrieve] :: problems summary ::
[ivy:retrieve] :::: WARNINGS
[ivy:retrieve] [NOT FOUND ] com.atlassian.sal#sal-api;3.0.3!sal-api.atlassian-plugin (1041ms)
[ivy:retrieve] ==== atlassian: tried
[ivy:retrieve] https://packages.atlassian.com/mvn/maven-external/com/atlassian/sal/sal-api/3.0.3/sal-api-3.0.3.atlassian-plugin
[ivy:retrieve] [NOT FOUND ] com.atlassian.httpclient#atlassian-httpclient-plugin;0.23.0!atlassian-httpclient-plugin.atlassian-plugin (147ms)
[ivy:retrieve] ==== atlassian: tried
[ivy:retrieve] https://packages.atlassian.com/mvn/maven-external/com/atlassian/httpclient/atlassian-httpclient-plugin/0.23.0/atlassian-httpclient-plugin-0.23.0.atlassian-plugin
[ivy:retrieve] ::::::::::::::::::::::::::::::::::::::::::::::
[ivy:retrieve] :: FAILED DOWNLOADS ::
[ivy:retrieve] :: ^ see resolution messages for details ^ ::
[ivy:retrieve] ::::::::::::::::::::::::::::::::::::::::::::::
[ivy:retrieve] :: com.atlassian.sal#sal-api;3.0.3!sal-api.atlassian-plugin
[ivy:retrieve] :: com.atlassian.httpclient#atlassian-httpclient-plugin;0.23.0!atlassian-httpclient-plugin.atlassian-plugin
[ivy:retrieve] ::::::::::::::::::::::::::::::::::::::::::::::
build.xml
<project xmlns:ivy="antlib:org.apache.ivy.ant" name="hello-ivy" default="ivy-get-binaries">
<target name="ivy-get-binaries">
<ivy:settings file="ivysettings.xml" />
<echoproperties prefix="ivy."/>
<ivy:retrieve />
</target>
</project>
ivy.xml
<ivy-module version="2.0">
<info organisation="foo" module="bar"/>
<dependencies>
<dependency org="com.atlassian.jira" name="jira-rest-java-client-core" rev="4.0.0"/>
</dependencies>
</ivy-module>
ivysettings.xml
<ivysettings>
<settings defaultResolver="atlassian"/>
<resolvers>
<ibiblio name="atlassian" m2compatible="true" root="https://packages.atlassian.com/mvn/maven-external" />
</resolvers>
</ivysettings>
Checking with Maven
Resolving the dependencies for jira-rest-java-client-core works fine using Maven:
<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">
<modelVersion>4.0.0</modelVersion>
<groupId>foo</groupId>
<artifactId>bar</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<name>minimal-pom</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.version>1.8</java.version>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>${java.version}</source>
<target>${java.version}</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>com.atlassian.jira</groupId>
<artifactId>jira-rest-java-client-core</artifactId>
<version>4.0.0</version>
<scope>compile</scope>
</dependency>
</dependencies>
<repositories>
<repository>
<id>atlassian</id>
<layout>default</layout>
<url>https://packages.atlassian.com/mvn/maven-external</url>
</repository>
</repositories>
</project>