In general it seems like if you keep ignoring videos from a given channel you're subscribed to, they will stop appearing most of the time in the default view despite the fact that you are subscribed, although they'll still appear if you go to the "subscriptions" view.

Basically in the default view I'm not sure it even makes much difference whether you're actually subscribed to a given channel or not; it seems like it's more about whether or not you've viewed the channel's videos recently.