On Palpatine being free with his inability to sense Luke, my take is that Palpatine and Vader are in a sense a couple (no not in that sense, though I can imagine they are on some tentacle wrapped website, possibly in the Far East) their lives are so closely intertwined they are married in the true sense of the word (joined together) but it's not a happy marriage it more a dance of death.

Palpatine is acting like a suspicious spouse, he isn't fully sure what Vader is up to (in the same way that the Jedi aren't in the PT) to some degree Luke is right that Vader himself doesn't know what he is up to.

Palpatine's strength in the Force as Luke says makes him over confident, he has got so far by being one step ahead of everyone but there is still a lot about Vader that even Palpatine doesn't quite get.

Vader has freely shared the knowledge about Luke being in the task force and in jealous spouse mode he is vocalising his suspicions that Vader is up to something to put Vader in his place, though I'm not sure how much Vader is actually aware he is being out of place, beyond the obvious Sith ambition to kill his master and take his place at some point down the line.

The dialogue itself however is ripe with unfortunate double entendres.

I don't know how Ian kept a straight face while saying some of those lines and James must have been laughing his drawers off in his sound booth.