I tried to add a draw.io diagram to one of my wiki pages, after drawing my diagram, I hit "save", entered a name for my diagram, and then it brought me back to my diagram (no error or any indication of anything amiss). I then hit "exit". It warned me that my changes would be lost. I figured this was a spurious error, but after hitting "ok", my diagram was, indeed, entirely lost.
I have tried this in two web browsers Firefox (38.0.5) and Chrome (43.0.2357.134) on a Fedora 20 Linux workstation, and on Chrome on a Windows VM all with the same results. However, a co-worker was able to create a draw.io diagram on the same page with no issue.
I tried looking at the web console when I did a save, and saw this error message: "TypeError: b is null mxEditor.js:1:4293"