It appears that some commit between ac408014 and b9dc8d1a (maybe 2f9fa1976a?) breaks the compilation of CASE forms in a function's tail position when some (but not all) branches in a body form contain a RETURN.
PS> (ps (defun foo () (case x ("bar" (if y (return t) nil)) ("baz" nil)))) "function foo() { switch (x) { case 'bar': if (y) { return true; }; //----------------- missing break; here case 'baz': return null; }; };"
Scott