I was able to reproduce this a couple of weeks ago but not anymore. It appears that we aren't rendering blobs in this testcase anymore so it might be that SVG filter improvements put this off the blob fallback path.
Bug 1603899 Comment 11 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
I was able to reproduce this a couple of weeks ago but not anymore. It appears that we aren't rendering blobs in this testcase anymore so it might be that recent SVG filter improvements put this off the blob fallback path.