Performing moveTo with x.0.0.0 subnets fails consistently

[MetroConductor]

Problem description:
When parsing a x.0.0.0 network address, in example 240.0.0.0/4, calling Network::moveTo() causes an exception.

Steps to reproduce:

1. Create a network using Network::parse, ie.: $network = Network::parse('240.0.0.0/4');
2. Call moveTo with a higher prefix length, ie.: $network->moveTo(5);

Desired result:
An array with two Networks should be returned.

Actual result:
In most cases, a IpException is thrown with the following message: "Invalid IP address format"

Additional info:
This behaviour can be observed for most x.0.0.0 networks, especially with a prefix length smaller than 8. Attached you will find my test script, detailing the failings: iptools_network_test.zip