Every 10 minutes all launcher icons show blank panel space for a tenth of a second (estimate). My eyes are usually drawn by the flicker and recording the time showed the flicker occurred every 10 minutes to the second.

Attempted several random fixes to stop this annoyance but none stopped or changed the 10 minute flashes. All the "disabled" were of course enabled options that had the flash before I started randomly trying fixes.

Stopped checkgmail process (I had set it to check mail every 10 min)
Disabled compositing
Disabled panel lock, Disabled panel auto increase length increase
Changed appearance theme from AuroraMint to Mint-X
Launcher tool tip disabled
Launcher config directory (~/.config/xfce4/panel/launcher-14) execute only
Launcher .desktop file in the directory changed to read only

Removed ~/.config/xfce4 while logged out. Logged in and selected default profile

None of these stopped the blinking. Though of course logging out and in changed the offset of the 10 minute cycle. While looking for a bug report or a fix online I found these other users reporting the same problem.

SweetLou with a screenshot of panel before and during the blink.
http://forums.debian.net/viewtopic.php?f=6&t=68567

SweetLou tries various fixes
http://www.linuxquestions.org/questions/linux-desktop-74/xfces-panel-launcher-icons-disappear-898222/

Vovka-Korovka confirms bug with same panel version as me (4.8.5)
http://forum.xfce.org/viewtopic.php?id=6240

Linux Mint Xfce 201109 64 bit update pack 3