Safari fails to honor system proxy PAC for certain requests

I have a system proxy PAC configured on my macbook. Safari doesn't honor it but only for certain type of requests. I verified that the same config if working for Edge and Chrome.

This request for example doesn't go through proxy:

PUT https://sdmntprnortheu.oaiusercontent.com/...

Content-Type: image/png

x-ms-blob-type: BlockBlob

Sec-Fetch-Site: cross-site

Origin: https://chatgpt.com

Safari: Version 26.1 (21622.2.11.11.9)

Macos: 26.1 (25B78)