As part of the big bug review for 16.04 LTS, I have tested this on 15.10 and the bug is still there.
In the case of Empathy, the first Alt + Tab to it doesn't raise it to the foreground, but the second one does.
In the case of Pidgin, Alt + Tabbing to it raises the window to the foreground the first time, but its window decorations are gone.
As part of the big bug review for 16.04 LTS, I have tested this on 15.10 and the bug is still there.
In the case of Empathy, the first Alt + Tab to it doesn't raise it to the foreground, but the second one does.
In the case of Pidgin, Alt + Tabbing to it raises the window to the foreground the first time, but its window decorations are gone.