Not sure if this is a bug or a design choice- currently, if you put a purple item into the forge, its purple affix will not bubble up the way craftable affixes do. This gives the mistaken impression that you have zero inventory of that shard. It would be desirable to bubble all affixes up for consistency and so that the player can see how common that shard is in his forge inventory. Optionally, use a different color (purple again?) to distinguish this uncraftable modifier from the gold craftable shards on the item.
Edit to add: T5 affixes also don’t bubble up, and should.