Custom video thumbnails lost after node_save

Whenever node_save is called (outside node edit form), any custom thumbnail that has been uploaded for videos is lost. This happens when I call node_save programmatically or using VBO (Views Bulk Operations) etc.
- (During node_save) When function emthumb_emfield_field_extra is called, in case 'update', variable $items[$delta]['data'] is null or non existent.
- (During node_save) When function _emfield_emfield_field is called, array $items[$delta]['data']['emthumb'] is empty.
- Default provider thumbnail is displayed normally.
- node_load loads correct data including the thumbnails
Any help would be appreciated. Thanks!