  We apply the recently proposed RMF(BCS)* ansatz to study the charge radii of
the potassium isotopic chain up to $^{52}$K. It is shown that the experimental
data can be reproduced rather well, qualitatively similar to the Fayans nuclear
density functional theory, but with a slightly better description of the
odd-even staggerings (OES). Nonetheless, both methods fail for $^{50}$K and to
a lesser extent for $^{48,52}$K. It is shown that if these nuclei are deformed
with a $\beta_{20}\approx-0.2$, then one can obtain results consistent with
experiments for both charge radii and spin-parities. We argue that beyond mean
field studies are needed to properly describe the charge radii of these three
nuclei, particularly for $^{50}$K.
