FULL PRODUCT VERSION :
sstory$ java -version
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
OS X El Capitan 10.11.3 (15D21)

A DESCRIPTION OF THE PROBLEM :
Before determining that this was a bug, I posted my problem here: http://stackoverflow.com/questions/35275239/marshall-unmarshall-nested-map-with-jaxb/35321306#35321306

In recap: If using JAXB annotations to marshall a POJO, and that POJO contains a java.util.Map field, annotating that field with @XmlElement results in:

java.lang.ExceptionInInitializerError
at com.digitalreasoning.datajetway.models.chat.ChatSession.<init>(ChatSession.groovy:24)
at com.digitalreasoning.datajetway.models.chat.ChatSession$ChatBuilder.build(ChatSession.groovy:144)
at com.digitalreasoning.datajetway.models.chat.ChatSessionTest.setup(ChatSessionTest.groovy:51)
Caused by: com.sun.xml.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions
java.util.Map is an interface, and JAXB can't handle interfaces.
this problem is related to the following location:
at java.util.Map
at private java.util.Map MyField.someMap
at Customer
java.util.Map does not have a no-arg default constructor.
this problem is related to the following location:
at java.util.Map
at private java.util.Map MyField.someMap
at Customer
at com.sun.xml.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:106)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:489)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:319)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1170)
at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:145)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
at javax.xml.bind.ContextFinder.find(ContextFinder.java:441)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
... 3 more

Omitting the annotation (and therefore accepting the default name, required=false, etc) results in correct marshalling.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
The code sample needed to reproduce is in the question here: http://stackoverflow.com/questions/35275239/marshall-unmarshall-nested-map-with-jaxb/35321306#35321306

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
  <myField>
    <someMap>
      <entry>
        <key>foo</key>
        <value>bar</value>
      </entry>
      <entry>
        <key>baz</key>
        <value>qux</value>
      </entry>
    </someMap>
  </myField>
</customer>
ACTUAL -
java.lang.ExceptionInInitializerError
at com.digitalreasoning.datajetway.models.chat.ChatSession.<init>(ChatSession.groovy:24)
at com.digitalreasoning.datajetway.models.chat.ChatSession$ChatBuilder.build(ChatSession.groovy:144)
at com.digitalreasoning.datajetway.models.chat.ChatSessionTest.setup(ChatSessionTest.groovy:51)
Caused by: com.sun.xml.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions
java.util.Map is an interface, and JAXB can't handle interfaces.
this problem is related to the following location:
at java.util.Map
at private java.util.Map MyField.someMap
at Customer
java.util.Map does not have a no-arg default constructor.
this problem is related to the following location:
at java.util.Map
at private java.util.Map MyField.someMap
at Customer
at com.sun.xml.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:106)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:489)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:319)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1170)
at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:145)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
at javax.xml.bind.ContextFinder.find(ContextFinder.java:441)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
... 3 more

ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.ExceptionInInitializerError
at com.digitalreasoning.datajetway.models.chat.ChatSession.<init>(ChatSession.groovy:24)
at com.digitalreasoning.datajetway.models.chat.ChatSession$ChatBuilder.build(ChatSession.groovy:144)
at com.digitalreasoning.datajetway.models.chat.ChatSessionTest.setup(ChatSessionTest.groovy:51)
Caused by: com.sun.xml.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions
java.util.Map is an interface, and JAXB can't handle interfaces.
this problem is related to the following location:
at java.util.Map
at private java.util.Map MyField.someMap
at Customer
java.util.Map does not have a no-arg default constructor.
this problem is related to the following location:
at java.util.Map
at private java.util.Map MyField.someMap
at Customer
at com.sun.xml.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:106)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:489)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:319)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1170)
at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:145)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
at javax.xml.bind.ContextFinder.find(ContextFinder.java:441)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
... 3 more

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
http://stackoverflow.com/questions/35275239/marshall-unmarshall-nested-map-with-jaxb/35321306#35321306
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Removing the @XmlElement annotation for my java.util.Map field