It appears that the solution Cosmo proposed earlier does work. It consists of saving the text from the RTF box as its own .rtf file, opening it, select all, copy, paste into cell, close and then delete the .rtf file.

The last problem I have is with the SetFocus method. It doesn't seem to work for RTF text boxes. Does anyone know why, or have another way to set focus? Currently I am setting the focus to the RTF text box in the initialization of the UserForm in which it resides.