The upcoming Linux desktop environment KDE Plasma 5 dropped the support of XEmbed tray icons a while ago (see for any further reading).

Teamspeak uses QT 5.2.x (error messages appearing while getting this thing to run without the QT libraries, you delivered with Teamspeak 3 Client said that it's some sort of 5.2), which seems not to support this new tray icon system.

It's very annoying not to be able to see if you are muted, speaking or anything just by looking at the tray and I would really like to have it back. According to Grässlin's blog entry, updating QT to a newer version (>= 5.4) should fix everything.