talk to your son... they go through phases like that, or because 1 parent may be stricter than the other, or the child feels that they other parent is not as nurturing nor understands them....
And ultimately, kids do feel more comfy with their Mom.
Its natural.
But... since your son is older... maybe ask him 'why' because it hurts Daddy's feelings. But your Hubby, should not make him feel bad about it... nor treat him negatively because of it... remember, he is ONLY a child. The adult is not the child.
But, point out to your son what "family" is. And you both love him etc.
Or, some kids feel that the other parent is a competition for them, for Mommy's attentions. Its a phase. But still, talk with your son about it.
No matter what the cause may be. Or it is just developmental based.
My kids, sometimes prefer me... because, I am around them more... and they say "Mommy is cozy..." kind of thing and 'Daddy is strict..." not that I am not.. .but he is seen differently than they see me. But I always talk to them about not ignoring Daddy... because it hurts his feelings... and he has his own way.... but I also give my Husband 'tips' on dealing with them. More of a 'woman' thing.... but kids NEED to bond with their Dad too.
And, your Husband should just try and participate in the routines... not in a forced way, but in a laid back way. Maybe his 'style' of things tweaks your son??? And, boys need to know that expressing themselves is good... and that they can.... they don't have to be all 'strong and silent' types... nor be stoic. Maybe your son does not feel comfortable with Daddy because he can't express himself with Daddy? Can your Husband express himself in a nurturing way? Boys need that too.
Many reasons 'why' your son is doing that. But it often happens in children, it being a phase. So talk to your son, find out why... or teach him about feelings and that it makes Daddy feel left out. Teach him 'empathy' and caring....
I taught my son that since he was 2-3 years old. He will actually know if someone has hurt feelings and go and tell them "I care about you...." if they feel bad.
A child has to be 'taught' those things.
Your Husband sure, he feels left out. But he is the 'adult' and should not feel at odds with his son... nor hold it against him. Your son is the child.
Maybe talk about it ALL TOGETHER... nicely and calmly. So your son understands about feelings... and that he can say how he feels and in conjunction with others.
good luck, just some ideas,
Susan