Have seen this problem on a couple of computers so thought it'd be fairly well known, but unfortunately can't find it mentioned anywhere online.
Basically, Safari Mac occasionally seems to stop interpretting HTML halfway through a page, just printing the HTML to the browser screen and then keeps going as normal.
Anyone else seen or heard of this? Is there any solutions - other than using FireFox instead? :)
Unfortunately the instance in question is a protected backend of an unreleased project so can't share it. I'll let you know if it crops up anywhere else.
The only blind guess I can make is that there's something going on on the backend that causes Safari to think the output is no longer HTML. Other browsers might be more tolerant and treat the entire output as HTML as long as it started that way. It'd be interesting to know if you could reproduce this by using only client-side HTML. Also, if you find out what caused this be sure to make note of it here.