The fritzing file format doc
https://github.com/fritzing/fritzing-app/wiki/2.1-Part-file-format
has that and a variety of other useful suggestions about Inkscape issues, but that said I found this while creating (which I haven't finished yet) my first part with much help from steelgoose and oldgrey. I'd been seeing the issue on the second (not the first!) edit of the part and when it did it to steelgoose when he was doing an edit of my part he discovered that font was set to zero length. With experimentation I finally got a part create that failed first edit then tried things (this among the first because of the suggestions in the format file) til I found a solution. Once
I get my first part properly finished I'm planning on writing it up as a guide to other people trying to learn to create parts because it is neither easy nor well documented.
Peter Van Epp