Followup to the solved bug mentioned at the bottom.
Using 1.8.3.641 on Win10x64:
Create new document in Publisher with image setting "prefer linked" (I've got the German version, not sure about the exact English terms here)
Drag'n'drop a PDF file into the document, it will be a linked file if you check it with the move tool (key "V").
If you use the node tool (key "A"), you can double click the linked PDF file in the document (not in the layers panel) to edit it in a new tab (the tab still (wrongly) says "embedded")
change something in that "embedded" PDF, close the tab (no "Save/Save as" is possible)
The publisher document shows the changed state of the linked PDF.
Save publisher document, close.
Reopen the document: The changes made to the linked PDF are lost.
Similar - now solved - bug: