Let us review the sources:
(1) First, no precise reference is given for Geldtheorie und Konjunkturtheorie (1929) for where Hayek “advocated a constant M instead of MV.” Furthermore, it does not necessarily even follow that Hayek supported central banks meeting demand for high-powered money, just because he “advocated a constant M.”All in all, the idea that Hayek was a “stable MV” man before 1932/1933 looks fairly tenuous to me. Maybe there is some convincing evidence that he was, but I have not yet seen it.
(2) Secondly, yet again no specific reference is given for Investigations into Monetary Theory (1925–1929), which, anyway, was never even completed or published (Klausinger 2012a: 45, n. 1) by Hayek.
(3) Thirdly, we have a reference to Prices and Production.
But I have already cited the relevant passage from this work and demonstrated that it does not say what the free bankers think it says:
Klausinger, Hansjoerg. 2012. “Introduction,” in Hansjoerg Klausinger (ed.). The Collected Works of F. A. Hayek. Volume 7. Business Cycles. Part I. University of Chicago Press, Chicago.
Klausinger, Hansjoerg (ed.). 2012a. The Collected Works of F. A. Hayek. Volume 8. Business Cycles. Part II. University of Chicago Press, Chicago.