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For me this always happens in IE 11 (and below) on our reCaptcha site
(Help->About reports: "Version: 11.0.9600.17905, Update Versions:
11.0.21 (KB3065822)" ) .
In fact, the google demo page also has this issue, so I'm pretty sure it's a Google problem (https://www.google.com/recaptcha/api2/demo):