Uhm, if an item shows the entity description ingame without this mod, and that description is missing/replaced because of the mod, it's an actual change of the item description. And not having informations about the placed entity in an item description, if they were there before, is basically the opposite of "extending" a description. I don't understand the dismissive answer.
Anyway, the issue isn't limited to entity-placing items. As I described before, the mod overwrites descriptions defined in locale files. You can easily reproduce the issue: Just make a simple mod that gives a description with a locale file (under "[item-description]") to any item that doesn't place an entity, e.g. an ammo item. That mod will only work if "Extended Descriptions" isn't active.
Or just check repair packs: Their vanilla description vanishes when using this mod.
As I tried to explain before: This mod sets the localised_description-field of items (in data-final-fixes.lua) which overwrites descriptions from locale files. In cases where that field had a value before, the code merges the values, but descriptions in locale files are never copied to it.