The title of this thread refers to Moose whereas your example uses Mouse. Moose behaves different in this example, so this might be considered to be a bug in Mouse?

Not inlining a constructor for test since it defines its own construct
+or.
If you are certain you don't need to inline your constructor, specify 
+inline_constructor => 0 in your call to test->meta->make_immutable
Use of uninitialized value $eg in print at test.pl line 14.
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