Unfortunately I have no idea when it started because I don't normally use Safari but had it open to do some troubleshooting of the Viglink add-on.
BTW, I'm using the default theme and these add-ons:
Add VigLink Code 1.0 (Disabled)
Amazon/Ebay Parser 1.2.6
Hotspots by Waindigo 1.1.1
Live Update 4.0.0
Newest Post First by Waindigo 1.0.4
Post Ratings 1.7.2
QuickSearch in Header 1.1.1
Register Email 3.1
s9e Media Pack 20150611
Show Deleted 2.1
SK Mark Thread as Thread 1.2.0
SV - Responsive Social Sharing Buttons Lite 1.3.4
[bd] Widget Framework 2.6.0-dev
[ITD] Add Custom Icon and Link with Tool-tip in Footer. 1.3.0 (Disabled)
Will have to do that when I've got my dev environment back up and running again. Fortunately it wasn't a user who brought it up and my analytics doesn't show anybody using Safari so it isn't a high priority item given that I discovered it on accident.
Hopefully I'll have it put back together again by the end of the week.