@Immutable class, failure when trying to define private static members

Attempt to add 'private static' field to a class that has been
annotated as @Immutable causes an error.

Groovy Shell (1.7.4, JVM: 1.6.0_20)
Type 'help' or '\h' for help.
------------------------------------------------------------------------------------------------------------------
groovy:000> @Immutable class AClass

===> true
groovy:000> @Immutable class BClass

ERROR org.codehaus.groovy.control.MultipleCompilationErrorsException:
startup failed:
groovysh_evaluate: -1: cannot modify static final field 'FOO' outside
of static initialization block.
@ line -1, column -1.
groovysh_evaluate: -1: cannot modify static final field 'FOO' outside
of static initialization block.
@ line -1, column -1.
2 errors
...

In Groovy 1.7.3 it does not cause an error.
Groovy Shell (1.7.3, JVM: 1.6.0_20)
Type 'help' or '\h' for help.
------------------------------------------------------------------------------------------------------------------
groovy:000> @Immutable class AClass

===> true
groovy:000> @Immutable class BClass

===> true
groovy:000>
...