When a workflow is associated to a list, a workflow status column is automatically created for that workflow. The column has the same name as the workflow association. But when an instance of the workflow is actually run, the status field on the list item remains blank, and is never set to a value.
This is a Bug in Office 365 Preview.

Workaround    The main cause of the issue is that the workflow status field is set to read-only. You can manually work around this by setting the read-only property to false.
In a SharePoint PowerShell prompt, run the following:
$web = get-spweb <my web url>
$list = $web.Lists[<name of list or document library>]
$statusField = $list.Fields[<name of workflow status field>]
$statusField.ReadOnlyField=$false
$statusField.Update()