(https://forum.vc-mp.org/proxy.php?request=http%3A%2F%2Fimg.vcmp.ml%2F%3Fdi%3D35AE&hash=0bd73cc536faf93a49a3d88ea67361303047a03a)
That isn't a bug. That's someone hosting a 0.4 server wait till it announced and then switching over to a 0.3 server on the same port.
0.3 servers are automatically removed on a periodic basis to avert the issues Thijn mentioned. There's also an unwritten policy in place that anyone announcing 0.3 servers on the 0.4 masterlist risks having the server IP blocked from the masterlist indefinitely.