docformatter doesn't correctly recognize the short form of anonymous hyperlink references (__ URI) as a special block, and merges them into the preceding paragraph:

     """[...]
 
     This graphics format generates terminal escape codes that transfer
-    PNG data to a TTY using the `kitty graphics protocol`__.
-
-    __ https://sw.kovidgoyal.net/kitty/graphics-protocol/
+    PNG data to a TTY using the `kitty graphics protocol
+    `__. __ https://sw.kovidgoyal.net/kitty/graphics-protocol/
     """

This breaks the reST, and makes Sphinx unable to correctly process the reference.

Note that this only affects this shorter form; the long form (.. __: URI) is unaffected. The following variation (correctly) remains unchanged by docformatter:

    """[...]

    This graphics format generates terminal escape codes that transfer
    PNG data to a TTY using the `kitty graphics protocol`__.

    .. __: https://sw.kovidgoyal.net/kitty/graphics-protocol/
    """

Bisecting brought up 7898b69 as the first "bad" commit, which is exactly v1.6.0. The earlier 917fed9 also changed the output already, but in a slightly different way and it was probably rewritten anyways.