For anyone else reading this, there is an accompanying post on the Ventrian support forums:
http://www.ventrian.com/default.aspx?tabid=118&view=topic&forumid=4&postid=34276
The underlying problem is a call to the DotNetNuke.Common.Globals.NavigateUrl() call. In this call, there are two arguments: one is an instance of TabInfo, the other is a tabId. Both of these values must correspond to the destination Tab, not the origin Tab.
This was the error with both the Ventrian and the MagicNews modules. Anyone else who is developing modules should note this, as the standard API is ambiguous on the difference.