I have heard from time to time people mentioning that sigma lenses are prone to fungus. Is this untrue or fact? Will sigma users please verify this?

Of course, the users must proper maintain the lens (like cleaning after use, keep in dry storage when not in use, careful handling during usage & so on) and own them over period of time before commenting on it.

Like to take this opportunity to find out about Di & Dg lens from sigma, are they the same? Can they be used on film camera as well without any implication?