Remove 'trusty' string from Synaptic

It plainly doesn't 'steer the user towards non-free software' which was the GNU FSDG criterion last time I looked. Nor is one common usage word a branding issue in any jurisdiction I know of (IANAL) or 'trusty' claimed to be by Canonical here

http://www.ubuntu.com/legal/terms-and-policies/intellectual-property-policy
.

I stand corrected - it's been patched in the latest release.

As per your Settings issue this has been fixed on my system (see screenshot). Please confirm by doing a

sudo apt-get dist-upgrade

And testing again. If the problem persists please say which desktop you're using, and how you installed it (i.e. package names and install tool used).

I fully upgraded the system but it hasn't been solved.

I am running GNOME Shell (GNOME PPA) and synaptic-0.81.1ubuntu1 installed from (belenos-updates)

I can't reproduce this here on two Belenos systems at that synaptic release level. Without looking at the synaptic code I would therefore assume you're seeing 'trusty' because that's an active release level in your system from the ppa. E.g. the 'stable' in my png is from jxself's kernel repo and not present on my other Belenos machine. In any event as per my first entry 'trusty' is not part of Ubuntu's trademark and trade dress claims so it is not an issue.