"Untitled window" on bottom panel?

[marko_s]

Yesterday I noticed that a previously unknown icon/thumbnail named "Untitled window" had appeared in the bottom panel (besides the Menu button). When I click it, nothing happens (it doesn't open up anything) and it does not respond if I right-click it and choose "Close". I can only make it disappear by logging out and in again. I have no idea which program could cause this.

Also, it only seems to appear in one workspace - if I switch to another workspace, it is not there.

Any ideas? It is just a cosmetic problem really, but an annoying one. It appeared after the system updated Firefox 13 to a newer version 14.

I use Linux Mint 13 64-bit with MATE desktop.

[xpander]

running compiz?
i think its some unity decorator stuff
at least i remember having it some time ago with compiz enabled.

i dont use compiz anymore to check out and also i dont have unity stuff installed. but might be worth to check out

[marko_s]

AFAIK I'm using only the "basic" MATE setup without any extra effects. I'm not sure if Mint/MATE uses some Compiz decorations as a default?

EDIT *checked out Synaptic really quickly*

I have the basic Compiz core packages installed, but I believe they come as default. I'm not sure if they are actually in use. I don't seem to have any Unity stuff installed.

At least today I haven't seen that particular "Untitled window" pop up after booting up. Probably just some freak window decorator hiccup