Oh yes ... the non-unique solution haunts me to this day as something discovered to late. Having hired someone to code a new shape of Sudoku, I was excited to pay the guy for what I thought was excellent work. Having paid and exchanged excellent ratings on rentacoder we each went our separate ways. Only later did I discover my lack of due diligence, and there was no recourse or help available, as the coder went unresponsive and I tired of daily checks and fixes of the generated puzzles.
Turns out the new (24 tiles or cells as you call them here) shape wasn't that challenging when solved like a standard Sudoku. Years later I have began to revive the idea as an interactive game, but that is a tale for another thread. You may experience the original flawed program at http://TopHatSudoku.com
The practice puzzles all have unique solutions and a printout is available at http://Botchee.com
This site looks great, and I will post more once I've had a chance to look around