The issue_263.py script was in the ticket to provide a test.

I'm adding the script here for reference. I don't think the URL or
scenario was especially unique, but it did exhibit the behavior and is
worth keeping around for reference.

tests/issue_263.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python3
+import sys
+
+import cachecontrol
+import requests
+from cachecontrol.cache import DictCache
+from cachecontrol.heuristics import BaseHeuristic
+
+import logging
+
+clogger = logging.getLogger("cachecontrol")
+clogger.addHandler(logging.StreamHandler())
+clogger.setLevel(logging.DEBUG)
+
+
+from pprint import pprint
+
+
+class NoAgeHeuristic(BaseHeuristic):
+    def update_headers(self, response):
+        if "cache-control" in response.headers:
+            del response.headers["cache-control"]
+
+
+cache_adapter = cachecontrol.CacheControlAdapter(
+    DictCache(), cache_etags=True, heuristic=NoAgeHeuristic()
+)
+
+
+session = requests.Session()
+session.mount("https://", cache_adapter)
+
+
+def log_resp(resp):
+    return
+
+    print(f"{resp.status_code} {resp.request.method}")
+    for k, v in response.headers.items():
+        print(f"{k}: {v}")
+
+
+for i in range(2):
+    response = session.get(
+        "https://api.github.com/repos/sigmavirus24/github3.py/pulls/1033"
+    )
+    log_resp(response)
+    print(f"Content length: {len(response.content)}")
+    print(response.from_cache)
+    if len(response.content) == 0:
+        sys.exit(1)