Re: mark not set after a yank

[Richard Stallman]

    Very often when I do a move of the point using M-< followed by a C-w emacs
    complains about the mark not being set. emacs-21.3 abd prior always seems to
    work as it should. My work around is to do c-x c-x and then c-w

    This seems to indicate the c-x c-x knows about the mark but not c-w

That is what would happen in Transient Mark mode, I think.
Is it possible you enabled that mode?