  The calcium isotopes have emerged as an important testing ground for new
microscopically derived shell-model interactions, and a great deal of focus has
been directed toward this region. We investigate the relative spectroscopic
strengths associated with $1f_{7/2}$ neutron hole states in $^{47, 49}$Ca
following one-neutron knockout reactions from $^{48,50}$Ca. The observed
reduction of strength populating the lowest 7/2$^{-}_{1}$ state in $^{49}$Ca,
as compared to $^{47}$Ca, is consistent with the description given by
shell-model calculations based on two- and three-nucleon forces in the neutron
$pf$ model space, implying a fragmentation of the $l$=3 strength to
higher-lying states. The experimental result is inconsistent with both the
GXPF1 interaction routinely used in this region of the nuclear chart and with
microscopic calculations in an extended model space including the $\nu1g_{9/2}$
orbital.
