Started seeing the same bug after upgrading to 18.04 LTS. It only
happens when I have some "security" update(s), indicated by red icon
color. After the updates are installed, the notification icon color
changes to blue (indicating normal non-security updates) but icon stays
in the tray, even though there is no further updates available. This
notification icon can only be cleared by leaving the KDE session.
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After update, icon stays in tray
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