have had this problem before.
and believe me it can have nothing with early entering although it some time can be the
cause but i dont think in your case.
i had a decent dog to fox that did this while running and it was just him being
frusted as he hated them that much.
all it did was hunt him as often as i could on them and he settled on them well
or even give him a few buunies first if you are out lamping .
my old dog would still do it when chasing them in thick cover in the day but.
hunt the f***k out of the dog and you might be surprised it worked for me.
all the best
macker