  Karl Popper published, in 1968, a paper that allegedly found a flaw in a very
influential article of Birkhoff and von Neumann, which pioneered the field of
"quantum logic". Nevertheless, nobody rebutted Popper's criticism in print for
several years. This has been called in the historiographical literature an
"unsolved historical issue". Although Popper's proposal turned out to be merely
based on misinterpretations and was eventually abandoned by the author himself,
this paper aims at providing a resolution to such historical open issues. I
show that (i) Popper's paper was just the tip of an iceberg of a much vaster
campaign conducted by Popper against quantum logic (which encompassed several
more unpublished papers that I retrieved); and (ii) that Popper's paper
stimulated a heated debate that remained however confined within private
correspondence.
