The first way it's unusual is that I can identify exactly when it was manufactured. This particular pattern was made between 1908 and 1920, but because it has an Italian tax stamp on it I can say with some certainty that it entered circulation on 30 Mar 1910. The stamp actually says "Ufficio del Bollo Strao 30 Mar. 910 Milano". If you're interested (although I don't know why you would be), the other stamp was used 1883-1914 and says "Regno d'Italia centesimi 30".
The second way the pack is unusual is that the glue bonding the card together is perishing. The backs have come off several of the cards. They're all present, they're just not attached. I haven't seen this happen to any pack of cards before, let alone one from a quality manufacturer such as Dondorf. Gawd knows what's going on there. Also, only two faces of the box came with the pack (the back and one end), but there's a piece of cloth that looks as if it was once part of the box before the cardboard came off it. I don't have any other Dondorf boxes with linen in them, but it has a Turnin-shroud-like impression of part of the opening mechanism for the box (were it present) so it does look to have been part of it.
Looking at the packs on offer on eBay these days, if I want to extend my collection of playing cards I'm going to have to get richer.