If "Icon" field contains 2 or more dots in name thunar don't show icon. For example "Icon=3d3b_model.0" don't work. Best regards.
Sure, because Icon values with dots are treated as file names. Use proper names for themed icons instead.
Stupid comment. U can't properly found the file extension? Just look from end of filename and find first dot... It is simply - just try =)
It'd be a bug if we would implement it otherwise. Just pick sane icon names and stop complaining.