Trust every time I connect my iPhone to my iMac?

During synch of iPhones / iPad, Finder asks me Trust my devices EVERY TIME I connect them for backup/synch

When I synch or backup my iPhones or iPad via USB, I am asked each time if I trust my iMac. Every time. Correct me if I am wrong, but that should only happen during the first setup.

Admittedly, I have been traveling quite a bit late reply and, as such, could only backup via WiFi, however my phones or iPad have never been hooked up directly to another Mac in my foreign apartment or to any other computer.

All devices have been updated to the newest software, but this occurred before that.

(As a memo: in Finder when I was synching/backing up, before the iOS update I could see the devices in the left side pane, but not the configuration content — i.e., backup, update, manually manage songs & content, etc. This resolved itself with the iOS update. Related?)