"Not a member: GetCurrentDatabase" error when forwarding from ND6 client to R5 client

Most of the users in my organization have been switched to Notes 6, but a few remain on Notes 5.

Several of the R5 clients have reported getting the following error message when opening memos from people who are using Notes 6:

“Not a member: GETCURRENTDATABASE”

Has anyone else seen any ND6 to R5 compatibility problems, particularly with mail? I can see that ND6 has this method for NotesUIWorkspace, but how could that possibly affect a Notes 5 client?

We’re running the iNotes template on both ND6 and Notes 5.