Chrome downloads the reloaded page on HTTP 205 response after an AJAX request
The closest I could find was that it might be a bug, because in this file: https://chromium.googlesource.com/chromium/chromium/+/trunk/net/http/http_stream_parser.cc
the comment starting at line 837 does not match the code at line 850: i.e. the comment doesn't mention that a 205 must be of zero length, but the code treats 205 like 1xx, 204, and 304. That was actually the only blink code I could find that mentioned 205 (outside of defining constants).
It might also be worth trying the latest Opera version; if the problem also happens there, it points the finger more strongly at a bug in the Blink source code.