One might be tempted to think that Pax has just become tolerant of Sylvie. That is undoubtedly the case, but it also seems that he has gradually become genuinely fond of her. He wags his tail at her approach, favors her with the occasional lick on the cheek, and even - to her absolute delight - sometimes comes to her when called. I have not yet been able to catch that on tape, but Sylvie has definitely added an emphatic "PAX!!" to her vocabulary.
All of this might well be due to the spoils Pax gets from Sylvie's high chair three times daily... whatever it is, it's good to see our two "kids" getting along so well these days.