It's not a bug.
What's happening is that the getPage() method defines an accessor for the $obj->Page property. So, in your PHP code, if you write $obj->Page, then it will get the value of that property by executing $obj->getPage().
Properties can't have arguments, so no arguments are ever passed to getPage() when it's used in this way.
The best solution here is to rename getCopyrightRange() to CopyrightRange().