When editing a post's tags today (directly, via the "Edit tags" link), the tag edits are successful, but instead of returning me to an updated page, I receive something like:
{"success":true,"html":"<a href=\"/questions/tagged/linux\" class=\"post-tag\" title=\"show questions tagged 'linux'\" rel=\"tag\">linux</a>< ... continues ...
This happened to me on U&L, and terdon has confirmed it also occurs for him on ELU.