I thought this was to do with the recent Libre Office update. Opening a file attached to an email in Kmail, Libre Office gave it a file name of "untitled 1". But today I tried it with a PDF, a .doc. and a .odt. Now they all open with a file name such as "messageviewer_gU2483", given a directory of root/tmp. After a few goes the directory goes to default Documents.
This is a very new bug - 377150 at https://bugs.kde.org/show_bug.cgi?id=377150.
This is a very new bug - 377150 at https://bugs.kde.org/show_bug.cgi?id=377150.