NullPointerException when including a submodule of a more recent revision than the module

Attached are two yang files, a simple module which includes a submodule. When parsing them a NullPointerException occurs:

java.lang.NullPointerException
at org.opendaylight.yangtools.yang.parser.builder.impl.GroupingUtils.getTargetGroupingFromModules(GroupingUtils.java:59)
at org.opendaylight.yangtools.yang.parser.impl.YangParserImpl.resolveUsesTargetGrouping(YangParserImpl.java:1083)
at org.opendaylight.yangtools.yang.parser.impl.YangParserImpl.build(YangParserImpl.java:707)
at org.opendaylight.yangtools.yang.parser.impl.YangParserImpl.parseYangModelSources(YangParserImpl.java:354)
at org.opendaylight.yangtools.yang.parser.impl.YangParserImpl.parseSources(YangParserImpl.java:195)

It only happens when the submodule has a more recent revision date than the module. The include statement in the model specifies no revision date.

When debugging I can see that
org.opendaylight.yangtools.yang.parser.builder.impl.BuilderUtils.findModule(QName, Map<URI, TreeMap<Date, ModuleBuilder>>) is unable to find the correct module.

The Yangtools version is 0.6.5-Helium-SR3.