While in creative mode, plants such as grass, roses, etc are not breakable with a sword as they are in survival mode.
This also appears to affect placed string (tripwire), cobwebs, and other things normally broken with a sword while in survival mode.
Linked issues
Comments 2
Indeed a WAI. MC-18368
I think this is a feature... Swords aren't meant to break anything in Gamemode 1.
Please correct me if I am wrong.