>> This patch fixes the error, but still e.g. in Info buffer
>> typing 'C-h m q' moves point in the Info buffer to some fixed position
>> (maybe related to a position in *Help* buffer), i.e. still something is wrong.
>
> Hm...  it doesn't seem like anything in `context-menu-map' should be
> moving point (unless there's a bug in some of those functions it's
> calling, which is possible)...

Actually, this was caused by thing-at-mouse that uses mouse-set-point
in bug#50256 (a detailed description added in bug#50256).

But regarding this bug#9923, and the question about avoiding :filter
evaluation for context menus - since the context menu is bound to 'ignore':

  `(menu-item ,(purecopy "Context Menu") ignore
              :filter (lambda (_) (context-menu-map)))

does it make sense to ignore 'ignore' like in this patch?