False captive portal detect?

[Steve]

> I then connected to a couple of external sites, such as vpn.uci.edu.
> They did not show the warning.  I didn't log in - just hit cancel at
> the prompt.  After that, I wasn't able to see the error again.

This is very interesting, after tried to connect to vpn.uci.edu, the error gone.
I never try cert from commercial CA, only install self-signed CA in my
system chain.