I find the network applet uses the wrong WiFi icon when the WiFi is disconnected. It instead shows a full-signal-strength connected icon. This is consistent across icon sets and is confusing to the user, eg:
The expected icon would be what GNOME uses, eg:
This is a small fix that will improve the user experience; if someone can let me know what/where to edit/patch, I can test the fix and prepare a pull request.
Guessing this must be related to your hardware because when I’m disconnected from wifi I see the normal disconnect network icon.
This did turn out to be the La Capitaine icon theme; my apologies for the noise!
Please raise an issue on the issue tracker for that icon theme so that it can be fixed. Just sounds like a symbolic link is missing to the network disconnect icon.