  The experimental PNC results in $^{18}$F, $^{19}$F, $^{21}$Ne and the current
theoretical analysis show a discrepancy . If one interprets the small limit of
the experimentally extracted PNC matrix element for $^{21}$Ne as a destructive
interference between the isoscalar and the isovector contribution, then it is
difficult to understand why the isovector contribution in $^{18}$F is so small
while the isoscalar + isovector contribution in $^{19}$F is relatively large.
In order to understand the origin of this discrepancy a comparison of the
calculated PNC matrix elements was performed. It is shown that the $^{18}$F and
$^{21}$Ne matrix elements contain important contributions from 3$\hbar \omega$
and 4$\hbar \omega$ configuration and that the (0+1)$\hbar \omega$ calculations
give distorted results.
