If you change max icon size px from 19 to 20 with panel size of 25, the last icon from right disappears from the system tray. I'm attaching 2 screenshots that show this behavior.
Created attachment 3319 Working with px 19
Created attachment 3320 Not working with px 20
This is with gtk-xfce-engine-2.7.0 and default "Xfce" theme. And with icon theme: http://tiheum.deviantart.com/art/Faenza-Icons-173323228 Faenza_Icons_by_tiheum.zip Quick download: http://trumpetti.atm.tut.fi/gentoo/distfiles/Faenza_Icons_by_tiheum.zip And the icon that disappers is xfce4-power-manager, 1.0.2
Created attachment 3321 Restart allocation if we overflow the number of rows
(In reply to comment #4) > Created attachment 3321 > Restart allocation if we overflow the number of rows This works. Thanks :)
Applied in 7659c5b.