Product Version: NetBeans IDE 8.1 RC2 (Build 201510122201)
Java: 1.8.0_66; Java HotSpot(TM) 64-Bit Server VM 25.66-b17
Runtime: Java(TM) SE Runtime Environment 1.8.0_66-b17
System: Linux version 4.2.0-16-generic running on amd64; UTF-8; en_US (nb)
User directory: /home/tkruse/.netbeans/8.1rc2
Cache directory: /home/tkruse/.cache/netbeans/8.1rc2

I click on 'download source' in the dependencies of a multi module maven project child module, Netbeans performs some checks but does not download the sources.

When using 
mvn dependency:sources 
from the command line it works.

The only things I found in the log that might be related:

INFO [org.netbeans.spi.lexer.MutableTextInput]: !!WARNING!! Missing READ-LOCK when accessing TokenHierarchy: input-source:org.netbeans.modules.editor.NbEditorDocument@1b04f05b, mimeType='text/x-maven-pom+xml', kitClass=null, length=7164, version=2, file=org.netbeans.modules.maven.grammar.POMDataObject@1fcb283f[/home/tkruse/arbeit/projekte/bpi-app/pom.xml@7c5cf6e0:9409dad]
java.lang.Exception
        at org.netbeans.lib.lexer.TokenHierarchyOperation.ensureReadLocked(TokenHierarchyOperation.java:406)
        at org.netbeans.lib.lexer.TokenHierarchyOperation.tokenSequence(TokenHierarchyOperation.java:431)
        at org.netbeans.lib.lexer.TokenHierarchyOperation.tokenSequence(TokenHierarchyOperation.java:427)
        at org.netbeans.api.lexer.TokenHierarchy.tokenSequence(TokenHierarchy.java:186)
        at org.netbeans.modules.xml.text.completion.XMLCompletionQuery.shouldCloseTag(XMLCompletionQuery.java:468)
        at org.netbeans.modules.xml.text.completion.XMLCompletionQuery.queryValues(XMLCompletionQuery.java:351)
        at org.netbeans.modules.xml.text.completion.XMLCompletionQuery.query(XMLCompletionQuery.java:127)
        at org.netbeans.modules.xml.text.completion.XMLCompletionProvider$Query.query(XMLCompletionProvider.java:124)
        at org.netbeans.spi.editor.completion.support.AsyncCompletionTask.run(AsyncCompletionTask.java:223)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443)
        at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68)
        at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058)




WARNING [org.openide.util.WeakListenerImpl]: Can't remove java.beans.PropertyChangeListener using method org.netbeans.modules.editor.NbEditorDocument.removePropertyChangeListener from org.netbeans.modules.editor.NbEditorDocument@3609746
e, mimeType='text/x-java', kitClass=null, length=3309, version=1, file=org.netbeans.modules.java.JavaDataObject@786f40f[/home/tkruse/.cache/netbeans/8.1rc2/index/s288/java/15/gensrc/org/springframework/integration/transformer/AbstractTr
ansformer.java@f8775987:143f6bea]
WARNING [org.netbeans.modules.java.source.parsing.JavacParser]: ClassPath identity changed for /home/tkruse/.cache/netbeans/8.1rc2/index/s288/java/15/gensrc/org/springframework/integration/expression/IntegrationEvaluationContextAware.ja
va@2057f430:99a936c, class path owner: null original sourcePath: /home/tkruse/arbeit/projekte/bpi-app/src/main/java:/home/tkruse/arbeit/projekte/bpi-app/src/main/resources new sourcePath: 
INFO [org.netbeans.modules.gsf.testrunner.ui.api.UICommonUtils]: File cannot be found for selected node: Test Dependencies.
INFO [org.netbeans.modules.gsf.testrunner.ui.api.UICommonUtils]: File cannot be found for selected node: Dependencies.
INFO [null]: Last record repeated again.