Concurrency and Static Method Hiding

In the code below, the UnsafeCounter class defines an increment method that hides the synchronized static method from the Counter superclass. What is the primary concurrency issue that arises from this design?

class Counter {
    public static int total = 0;
    public static synchronized void increment() {
        total++;
    }
}

class UnsafeCounter extends Counter {
    public static void increment() {
        // Overridden without synchronization
        total++;
    }
}

public class StaticTest extends Thread {
    public void run() {
        for (int i = 0; i < 1000; i++) {
            UnsafeCounter.increment();
        }
    }
    
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new StaticTest();
        Thread t2 = new StaticTest();
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("Total: " + UnsafeCounter.total);
    }
}