Spaces imported from 5.1.x into OnDemand lose user data

The "Import Spaces" page in Confluence 5.2-OD-14-1 says:

The current Confluence OnDemand accepts back-ups from version 5.1 and newer releases.

And, while it does allow the import of a 5.1.x space, all the pages will show up as being created by 'Anonymous', even if the username of original creator of those pages exists in both systems.

I've attached a simple space export from Confluence 5.1.5 with pages made by a user 'admin' to illustrate the problem. Simply ensure an 'admin' user exists in Confluence OnDemand and import this space. All the pages in the space will have been created/modified by 'Anonymous'.

In the database it will look like this:

 contentid |                    title                     | creator
-----------+----------------------------------------------+--------
   2129923 | Importable Space Home                        | NULL
   2129922 | This is admin's page                         | NULL

Either we need to disallow the importing of spaces from Confluence 5.1.x (and adjust the messaging on the page to indicate this) or we need to fix the importing of the user data.