That bug has been opened on https://launchpad.net/distros/ubuntu/+source/gnome-panel/+bug/42772

"graphical annoyance : I once positionned clock applet "0 pixel" near mixer applet. As time passes by, due to the non-monospaced font, clock label is larger at certain times (22:22 is larger (pixel-wise) than 11:11 for example).

The applet does not reclaim "free space", so there is a gap (apparently empty space, but in fact it is embedded in the applet) between clock and mixer :

http://deep-ocean.net/captures/clock/clock-applet-padding-right-4.png

(notice the -normal- 2 pixels left-padding and the -too large- 4 or 5 pixels right padding when doing mouse-over)

I think the applet should reclaim this unused space. I remember it did in GNOME 2.12, but i could have been dreaming it did ;)

Occasionnaly, right clicking on the applet at different times of day makes it actually reclaim this "free space", but it doesn't happen every time i try (it seems to work only when I have not clicked for a long period of time, but i can't confirm this).
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> THanks for your bug. What version of Ubuntu do you use. That looks like a minor detail, updating settings according to that. The screenshot has not gap between the applets, do you speak of the gap of the clock applet between the label and applet border?
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Dapper, kept up-to-date every day. Yes, i speak about the gap between label and applet border."