[Zope-CMF] Portal type = None

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For some strage reason during the upgrade from CMF 1.2 to 1.3, most of my 
portal documents have lost their type definition. When I go to the workflow 
tag for these documents it says:
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This object's portal type is: None.

This object doesn't belong to any workflow.
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Even stranger is the fact that I run two different CMF instances, but only 
the oldest one is affected.

Is there any way I can programatically change the portal type on these 
documents?
I hate the idea of having to manually recreate hundreds of docs :(

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