[CentOS] unexpected 'reinitialize disk?' prompt form anaconda during kickstart with zerombr

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Anyone have any thoughts on why anaconda might be prompting me to
reinitialize the disk during the kickstart of a Centos6.4 install on
hyperV when
a) the kickstart file contains "zerombr" as referred to in the
installation guide[1]
b) installation proceeds with no prompt on KVM hypervisors and succeeds?

I have read the release notes[2]/tech notes[3] for 6.4 and noted lots
of changes concerned with virtualization in general and hyperv hosts
in particular, but I don't see anything that appears to be directly
pertinent.

I did try using the "clearpart --initlabel --all" approach (although
that appears to be removed from 6.4), but I get the prompt with that
as well.

[1]:
https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Installation_Guide/s1-kickstart2-options.html
[2]:
https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html-single/6.4_Release_Notes/index.html
[3]:
https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/6.4_Technical_Notes/index.html
- -- 
Duncan Hutty
http://www.allgoodbits.org
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