I think I understand this, but if what I say below is incorrect, someone please correct me.
Rares can't be drawn by discarding effects of common cards, though they can be drawn on their own. So Supply Units, for example, will never replace the soldier you discard with a rare, though it does allow the next card after Supply Units to be rare.
Druid is not affected by this rule at all, as it doesn't discard cards. As is normal, the next card after Druid can be rare if you're lucky. The other card, which you choose via mode, is not a "discard" mechanic--it's a "replace" mechanic. Therefore, the replacing card can be rare (also if you're lucky).
This looks to me to be the card working as intended in the rules.