xfce panel launcher does not accept icons from file

[crappuccino]

i have this weird problem that the quick launchers in my xfce panel have the "missing icon" pic whenever i choose an icon for them from a file. the corresponding files all exist, are readable and display correctly in the whisker menu.
launcher icons display correctly when i choose an icon from the category presets ("select icon from -> any category"). but as soon as i choose "from image files", my choice is disregarded no matter which file i pick.
when i click "help" to find out what the launcher app is called, a window opens and immediately crashes. is it a part of xfce4-panel? because i don't have xfce4-quicklauncher-plugin installed (what's that?).