Error Compiling Vaadin WidgetSet

I am trying to use the Maven GWT (2.6.0) plugin to compile a WidgetSet that inherits com.vaadin.DefaultWidgetSet. I am using Vaadin 7.1.11 and have no GWT-based dependencies other than Vaadin and the Maven GWT plugin. I am getting this error on compilation:

[font=courier new]
[INFO]
Loading inherited module ‘com.example.hello.WidgetSet’
[INFO]
Loading inherited module ‘com.vaadin.DefaultWidgetSet’
[INFO]
Loading inherited module ‘com.vaadin.Vaadin’
[INFO]
[ERROR]
The value opera was not previously defined.
[INFO]
[ERROR]
Line 64: Unexpected exception while processing element ‘set-property’


Any help would be much appreciated.

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Maybe this is related:

“Changing permutations (ie6 and opera are gone, ie10 was added, note that newer versions of opera are webkit based and do not need their own permutation)”
http://stackoverflow.com/questions/21517007/gwt-2-6-with-gxt-3-0-1-error-in-compile

I would recommend sticking to the Vaadin plug-in for compiling the widgetset as far as possible.

The GWT plug-in might automatically include dependencies to GWT artifacts in addition to the Vaadin artifacts that contain the same classes, which could cause classpath issues. This was an issue at least with older versions of the GWT plug-in, not sure if still the case.