That is one aspect I dislike about Castle even though I love it overall. I wouldn't mind if they put in a few minutes say every other episode for the ongoing arc ala Burn Notice/White Collar. Castle seems to only have them every so often and mostly in the finale/premiere. It helps with that whole sudden jumping between "here's our fun murder of the week" and "oh wait, everyone could die serious time!"
I get that they like to "nod" to the hiatus but they do pick up instantly as if they really hadn't spent any time apart, and this wasn't the first time they've done that to start a season.