UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.87 Safari/537.36

Steps to reproduce the problem:
1. Configure IE to use a PAC file
2. Open Chrome
3. Try and access a website blocked in the Proxy such as Facebook/Twitter > It brings up the web page
4. The blocked sites open
5. Check chrome://net-internals/#proxy
6. Clear bad proxies
7. Try and access a website blocked in the Proxy such as Facebook/Twitter > Its blocked

What is the expected behavior?
Blocked websites should never be shown in any browser configured to use the PAC file. IE/Firefox behave as expected > The sites are always blocked.

What went wrong?
In Chrome sites blocked in the proxy are gaining access via DIRECT route because the good proxies are being marked as bad. Manually clearing the bad proxies seems to work every time and also waiting for a period of time (say 10 mins plus) seems to then start routing traffic through the proxies.

Did this work before? N/A 

Chrome version: 49.0.2623.87  Channel: stable
OS Version: 10.0
Flash Version: Shockwave Flash 21.0 r0

There are several similar tickets logged but none describing this exact problem. Why are proxies identified as bad when they are clearly functional? How can we stop proxies from being marked as bad? Thanks