You’re right, I’ll get this changed right away!
Cr_nch is right, Greenhouse used to be the main meaning but since we’ve changed it, we now simply have it as an accepted meaning for those who learnt it that way which ends up overriding the automatic warning. I’ll double check with the team though to see if we want to keep it that way.
Update: You should now get the “Oops, we want the kanji meaning, not the radical meaning.” message. The ‘Greenhouse’ was still being accepted as we had allowed it before we made the changes to how we handle user synonyms. Thanks for bringing it up!