Data disk gets ignored when creating a new virtual machine

Hi there,

I'm trying to add a new VM role to an existing cloud service. The new VM is added, but the data disk portion seems to be ignored. It's really strange, because if the request was bad I'd expect the whole thing to fail, but the VM gets created and comes up fine (other than missing the data disk). I read here that if you use a VMImage, the data disk is ignored, but that's not the case here - I'm using an 'official' image.

Here's the XML document I'm POSTing to the API:

<?xml version="1.0"?><PersistentVMRole xmlns="http://schemas.microsoft.com/windowsazure" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"><RoleName>dssdb720528</RoleName><OsVersion i:nil="true"/><RoleType>PersistentVMRole</RoleType><ConfigurationSets><ConfigurationSet i:type="LinuxProvisioningConfigurationSet"><ConfigurationSetType>LinuxProvisioningConfiguration</ConfigurationSetType><HostName>dssdb720528</HostName><UserName>xxx</UserName><UserPassword>xxxxx</UserPassword><DisableSshPasswordAuthentication>false</DisableSshPasswordAuthentication><SSH><PublicKeys><PublicKey><Fingerprint>E46AA4E81832E51A2BE8B4C2907EF7A8024CEF6C</Fingerprint><Path>/home/xxx/.ssh/authorized_keys</Path></PublicKey></PublicKeys><KeyPairs><KeyPair><Fingerprint>E46AA4E81832E51A2BE8B4C2907EF7A8024CEF6C</Fingerprint><Path>/home/xxx/.ssh/id_rsa</Path></KeyPair></KeyPairs></SSH></ConfigurationSet><ConfigurationSet i:type="NetworkConfigurationSet"><ConfigurationSetType>NetworkConfiguration</ConfigurationSetType><InputEndpoints><InputEndpoint><LocalPort>22</LocalPort><Name>SSH</Name><Port>43120</Port><Protocol>TCP</Protocol></InputEndpoint></InputEndpoints><SubnetNames><SubnetName>Production</SubnetName></SubnetNames></ConfigurationSet></ConfigurationSets><AvailabilitySetName/><Label>ZHNzZGI3MjA1Mjg=</Label><DataVirtualHardDisks><DataVirtualHardDisk><HostCaching>None</HostCaching><DiskLabel>dssdb720528_data</DiskLabel><DiskName>dssdb720528_data</DiskName><LogicalDiskSizeInGB>40</LogicalDiskSizeInGB><MediaLink>https://xxx.blob.core.windows.net/vhds/dssdb720528_data_disk_2014_09_26_18_36.vhd</MediaLink></DataVirtualHardDisk></DataVirtualHardDisks><OSVirtualHardDisk><MediaLink>https://xxx.blob.core.windows.net/vhds/dssdb720528_os_disk_2014_09_26_18_36.vhd</MediaLink><SourceImageName>b39f27a8b8c64d52b05eac6a62ebad85__Ubuntu_DAILY_BUILD-trusty-14_04_1-LTS-amd64-server-20140923.1-en-us-30GB</SourceImageName></OSVirtualHardDisk><RoleSize>Small</RoleSize></PersistentVMRole>