Another vote for BenRG on this matter.
Marten realizes he's got a keeper this time, possibly lifelong, and that changes your perspective on what is and isn't acceptable around your better half. He's grown and changed over nearly 3000 strips; it's about time is all I can say. Then add to this the whole idea that Pintsize's mission really is almost over... ?
I'm with Ben on this, too, and Snarkyone's assertion that this is something built versus accidental. He seems more invested in this relationship. I'm not sure that either of them are thinking lifelong, but Marten, at least, is a lot more focused in the here-and-now than we've seen him in a long time (possibly ever).
Mission over? Not sure about that. Yes, he's mentioned that his role in Marten's life is different than it was and that he can kick back a bit now. But what we've seen in-comic about AIs is that their existence isn't quite that utilitarian; they have inner lives, friendships, et cetera, so even if Marten doesn't "need" Pintsize the way he used to, they're still friends.
And now I'm thinking Star Trek, and wondering what Pintsize's next five-year mission will be...
(PS: Howdy, presumed fellow Clash/Strummer fan!)