This change is done on purpose.
From the PHP manual:
"Dropped abstract static class functions. Due to an oversight, PHP 5.0.x and 5.1.x allowed abstract static functions in classes. As of PHP 5.2.x only interfaces can have them."
I believe you could make yourself in trouble when using it, and that's why there is a warning with strict.
It does make sense, because overloading is something that works on classes, and static functions do not reference classes.