OK, Think I've found the problem - it's a browser+ad blocker issue, which is presumably preventing pop-ups. I've now disabled Adblock Plus specifically for weatherlink.com (on Win10/Chrome) and the request to print is now able to open a new tab showing the report as a PDF. I suspect that what happens on any given PC will depend on the browser set-up, whether pop-ups are blocked and on how PDFs are set to be handled.