Lie algebras and failure of PBW

Dear Friends and Colleagues On p. 331 of Magnus-Karras-Solitar, Combinatorial group theory there is a hint at an unpublished manuscript of R. Lyndon [1955] containing an example of a Lie algebra over an integral domain for which the statement of the PBW theorem is not true. I did not find this example in the literature not did I find any other hint at it. Does anybody know anything about it? Many thanks in advance Johannes