Comment: the Adobe Flash Uninstaller appears to be messing with Opera's browser settings.
This has occurred for about the last month or so, after going through the Flash plugin update process (uninstall the old version, install the newer version).
This is with the Windows Opera web browser. Does not happen with Firefox.
Windows 10 64-bit, version 1607, build 14393.351.
Specifically: After uninstalling the Adobe Flash plugin, Opera "forgets" that the startup page was previously set to "specific page: about:blank"
and also: the specified download folder location setting.
Flash Player installer/uninstaller do not modify the browser settings in any way. I attempted to reproduce (same OS) and Opera 41.0 (latest) and was unable to reproduce. Something else is resetting the your home page setting, but it's not Flash Player uninstaller.