Ok, it should be fine now, please reraise any issue if not.

Ok, both trivial problems fixed (has correct reference sol, and only generates correct characters). I am rewriting the random generator now to make it more stringent.

I didn't know that was approved, I took the post down just after I read the issues below as I had to rewrite the generator. I will fix it now.

Fixed.

You are right. It doesn't make sense for the starting index to be larger than ending index. CW is slow right now, but will fix.