I separate my top panel into two separate panels (top left corner and top right
corner), in order to allow Beep to sit between them (see attached screenshot 1).
Recently I've been having problems of the top-right panel becoming 'unstuck'
from the corner if applet displays expand and contract in width. If a panel is
placed in the top right corner, it should stay there regardless of
additions/subtractions to it.

To reproduce:
- Change Clock preferences to show date (screenshot 2). Panel expands accordingly.
- Change Clock preferences back to remove the date (screenshot 3).  Panel
contracts towards the left, pulling the right edge away from the corner of the
screen.

Notes:
- this does NOT happen if you show and hide seconds from the Clock display.
Possibly because they're part of the same text area within the applet, possibly
because they're added towards the right, I'm not sure.
- this use case is not very common, but I used it for ease of reproduction since
the Time applet is included in Gnome. I am, however, experiencing it very
frequently with the 3rd party "Timer applet", which I'm using as a tea timer and
such. The newest verison normally displays only a greyed out clock icon, and
adds a countdown display only when a timer is activated. When the countdown
completes, my panel comes unstuck.
- tested on Ubuntu Dapper

Other information: