Created attachment 259745 [details] test page Safari does not allow for you to use a blob uri as a source for external media (e.g. use's xhlink:href). This is useful for clientside created assets, as well as as a feature test to detect SVG external media support. It seems to be attempting to request it from the network as it shows as a 404 error in the network tab. All other browsers that support the file blobs and createObjectURL are able to do this. I have attached a test page showing the issue.
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.