nm-applet shows wrong symbol: wired instead of wi-fi

[Michael Leetz]

Since the upgrade from Linux Mint 17 to 17.1 Cinnamon-edition the nm-applet often shows a wrong symbol: I'm connected via wi-fi, but it shows, that I'm connected to a wired network. This appears not in every session, but maybe in every third or fourth session of Cinnamon.
In /home/[user]/.xsession-errors I've found the following two lines:

"nm-applet-Message: using fallback from indicator to GtkStatusIcon"

"Cjs-Message: JS LOG: network applet: Cannot find connection for active (or connection cannot be read)
failed to create drawable
Cjs-Message: JS LOG: network applet: Found connection for active"

My wlan-card is Broadcom: BCM43224 802.11a/b/g/n

It does no matter, if I use the bcmwl-kernel-source or not. The problem occurs with the proprietary and the opensource driver.

Is this a known issue? And what to do to avoid this mistake?