Unable to import java.io into a scala package in a mixed scala/java project - scala

Question

I have a mixed scala/java project. Why would the following import not work?
This error occurs both in Intellij and more importantly on maven command line using
mvn clean -DskipTests package
Here is the intellij SDK:
Here is the relevant section of the pom.xml showing the java/scala interaction - as recommended by https://davidb.github.io/scala-maven-plugin/example_java.html :
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>4.1.1</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
</plugin>
</plugins>
</pluginManagement>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<executions>
<execution>
<id>scala-compile-first</id>
<phase>process-resources</phase>
<goals>
<goal>add-source</goal>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>scala-test-compile</id>
<phase>process-test-resources</phase>
<goals>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
<executions>
<execution>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
Here is the error from maven command line:
[ERROR] /git/OCspark/tcpclient/src/main/scala/com/pointr/tcp/iotest/package.scala:2: object io is not a member of package com.pointr.tcp.java
[ERROR] import java.io._
[ERROR] ^
Update Based on a comment by # LuisMiguelMejíaSuárez I looked at the java sources. Note that java is not the root of the package hierarchy - which might have then been the more obvious cause of this problem:
But .. unmarking_ the java directory as sources does fix the problem..
Why would this fix it?