Try to test it with comparison without talent and with.
The stealth tooltip should even have it there where it says 50% increased dmg and 20% increased speed, but right now it just says 20% increased speed, nothing else.
Even comment:
The damage increase portion of the talent is straight forward. Despite what most info says from old patches and other sites this does actually work with all damage from stealth that I have tested. Ambush, Garrote, Rupture, Fan of Knives, Crimson Tempest, Throw, Evicerate/Envenom and your specs combo builder. ( Source: https://web.archive.org/web/20140510034532/http://www.db.pandawow.me?spell=14062#comments )
Should be kinda easy to fix it.