Can't Reroll Champion Shards

When I right click a champion shard and choose to reroll it opens up the reroll thing where you insert 3 of something. But then I can't drag any further champion shards into it. Right clicking and choosing to reroll a different champion shard resets the whole thing, leaving me with just the 1 new shard choice in the reroller, still unable to drag more shards in. This means I simply can't reroll champion shards.

Am I just missing something or is this a bug?