Probably that's the formula for Ancient Socketed items. That editor is generating the item hex code from what you're giving in the editor.
1E 00 5A 00 00 00 00 30 FF 00 12 B8 B8 B8 B8 B8 00 00 0C 8F FF FF FF FF FF FF FF FF FF FF FF FF -> 32 Bytes (I'm guessing this is the correct ancient item hex code).
If FF is Ancient item setter byte, then the Item should be generated with Ancient options and not Sockets options.
Not sure if S16.1 is accepting this item and I think the calculation is done on that FF if you have 2 different items using the same byte. (Ancient + Socket)
What's happening if you have a normal Socketed item. The Ancient item setter byte is still FF or is changing/different?