Thanks for this workaround. It did help me on this occasion. But, of course, it's not a replacement for debugging in general. On this occasion I ended up dereferencing the links to the external files and so I do not run into the problem. Again, that's not a solution, just a workaround.
I did not fully investigate the problem, but I used the libraries to look into a file written out from LibreOffice and there the external references use shared strings. Might have something to do with what I'm seeing here...