Is it, though? If the instructions in your "How to start?" section don't work, that feels more like a bug. I went through all the exercises and didn't find a point where this was relevant.

Currently, the initial HEAD actually contains the solution for a future exercise. It was also created by a different user than the rest of the exercises.

Maybe the detached HEAD should contain a README with instructions like "You are in detached HEAD mode, reach the master branch to continue"