Last night, I was having really horrible packet loss. It was
typically 4% to 12%, with spikes over 60%. I found that this made it
practically impossible to stay invisible with Shauri's. (I am level
31 and have a wind skill of 158 or better, so under normal conditions,
it's not a problem.) However, although I often saw the blue "You have
become visible" message, it rarely--if ever--followed the red "You
feel yourself starting to appear" message.

I'm speculating that the client is trying to get a packet through that
says "Hey! I'm still singing Shauri's." However, if this packet
keeps disappearing into the ether, then the song interval times out on
the server, and the server figures I've stopped singing, so I become
visible. Eventually, the client manages to get the packet through,
and a soft mist surrounds me again.

In any event, the lessons I learned are:

1) When it says "you feel yourself starting to appear," you probably
won't become visible.

2) When it doesn't say "you feel yourself starting to appear," you
still may very well become visible.

Purna Hodari of Quellious