Refused to set unsafe header "Connection"

[polanskiman]

Not entirely sure what this means, but I keep getting this error in Safari's Web Inspector:

Code:

Refused to set unsafe header "Connection"
setRequestHeader ([native code], line 0)
setRequestHeaders (prototype.js, line 721)
request (prototype.js, line 690)
initialize (prototype.js, line 668)
(anonymous function) (prototype.js, line 20)
ActivityReminderCallback (general.js, line 3175)
(anonymous function) (index.php, line 1634)