To write them down quickly...
1/ the message icons changed to .png, but in the admin interface, they're refered to as .gif
=> error cuz it can't find them
2/ set an icon for a single board (i.e. 'thumb up' for Feature Discussion), and change its setting to 'first'
=> test a new topic: it ain't first, 'standard' still is...
/me almost never uses message icons... (disclaimer :D)
Should be fixed.
Site should be updated as well