When I copy a URL with ViewParameters in Firefox. The Url will be UTF8 encoded. So the brackets are %28 and %29
E.g.: http://www.example.tld/site/(param)/value -> http://www.example.tld/site/%28param%29/value

The new stack can now not match the route and give it to the legacy. There it can be matched.

When I look in the code I see, that the rawurldecode function has been used only for the semanticPathinfo:
https://github.com/ezsystems/ezpublish-kernel/blob/2267c6e903c38b027b3b97e2901ccf0923bcbbad/eZ/Publish/Core/MVC/Symfony/Routing/UrlAliasRouter.php#L126

In legacy it works because of:
https://github.com/ezsystems/ezpublish-legacy/blob/e6c912113a8cee636070d2ac1fcbd308f713b97e/lib/ezutils/classes/ezuri.php#L224