Empathy not opening on correct tag in Awesome-WM

Question

I have created a rule for my instant messenger, empathy, to always start on the "im" tag.

{ rule = { class = "Empathy" },
    properties = { tag = tags[1][5] } },

At the end of rc.lua, I auto-start it using:

awful.util.spawn("/usr/bin/empathy")

However, when restarting Aweseome-WM, the window always opens on the first tag.

Other programs work just fine:

    { rule = { class = "Firefox" },
        properties = { tag = tags[1][1] } },
    { rule = { class = "Codeblocks" },
        properties = { tag = tags[1][2] } },

I found someone describing the same problem here, and tried what was suggested (checking the window's class in an event) and I also checked the window's class using xprop, both methods tell me that "Empathy" is the correct class.

c:connect_signal("property::class", function(c)
        naughty.notify({ text = "CHANGED name!" .. c.class })
    end)

How can I make empathy appear on the "im" tag?