In challenges, you can use the "Tinker parts" menu, which can make things a little too easy, because you can litteraly set your crafts weight to zero (well, allmost zero, but thats for another bug report) which alows you to complete challenges pretty easely. (I beat the speed chalnge in a few seconds with this)
Sorry for spelling
Some would agree with this, some would not. I wouldn't call it a bug. Here is a suggestion out there that is along these lines, so feel free to upvote it if you like it!