I just observed something curious while playing level 22 "Solar Flare" in Dark Matter mode: I accidentally sent a flower to an enemy asteroid (I had a flower and a mine on the same asteroid and apperantly clicked the wrong one).
Once it arrived there (there werent any enemy seedlings around so it didnt get shot down right away), the first thing i observed was that the defense tree there didnt shoot at the flower, but I didnt mind that much. What did surprise me, however, was that the two icons for planting the flower showed up, albeit the menu bar didnt widen so the buttons were behind the text. Nonetheless, out of curiosity, I clicked the "Enhance defense tree" button -- and the Flower actually planted! It behaved as it would on any of my own asteroids. Only when it had attached to the tree, it changed its color to the enemy's.
I havent tried reproducing the error, but since i observed it quite precisely i think this counts just as well.
Might want to look up if you make sure the asteroid is really the player's before he can plant a flower