Well I've played around with this and here's what I've found.

If popup(sel)folderpix isn't specified, this works:

*popup "some Text" !DynamicFolder:"$Programs$"
*popup "some text" $filemanager$
*popup "some text" !Dynamicfolder:"$LitestepDir$LSDocs\*.htm
+these with custom icons..

If popup(sel)folderpix is specified, it obviously won't show any icons for folders, but it will also not show any custom icon either. This is quite reasonable cuz if you use folderpix you probably have the icon embedded in the image. I haven't tried specifying an arrowimage to see how that works, but I think it will. I BTW have the same build as you.