Yes, I agree it's more likely a change made to the construction of the Zen page which is now initiating this pop-up alert for some of us.
If you do a Google search using "getting rid of this page displays both secure and non secure items alert"
you'll find there are a number of threads on various IT forums on this very issue.
One suggestion I came across for getting rid of the alert (disclaimer: I have not tried this out, myself, nor am I recommending that you or other readers try this, you would need to do some cross checking first on reputable sites for the implications of changing these settings) was:
Go to: IE, tools, options, security tab, internet, Custom Level button, enable "access data sources across domains" or "access sub-frames across domains"
to which another contributor had added that they had also enabled
"Display Mixed Content"