Interestingly, today I tried a new fresh install in a virtual machine and I did not experience the URL forwarding behavior. I then copied the "%USERPROFILE%\AppData\Roaming\Opera Software" folder from the virtual machine and used it to replace the same folder on the physical machine. This did not resolve the issue. I then proceeded to do the same with the "%USERPROFILE%\AppData\Local\Opera Software" folder. This, too, did not resolve the issue on the physical machine. Finally, I did the same with the "%USERPROFILE%\AppData\Local\Programs\Opera" folder, and finally this did solve the issue.
Still not sure what all this means. It seems strange that two different fresh installs would behave differently like this. Equally strange that the URL redirection does not appear to have an exogenous cause, e.g. an anomaly with the operating system configuration or network configuration, as copying the "%USERPROFILE%\AppData\Local\Programs\Opera" folder from the virtual machine to the physical machine resolved the issue.