Mosaic puzzle problem

[ScacchoMattho]

After solving it, I cannot put the last piece, taken from the dragon , into its place: up-left.
Can someone help me?

[Dadelus]

The last piece goes into the upper right. If you have the upper left then you have not solved the puzzle.

[ScacchoMattho]

My mistake, it's the upper right piece that is empty. I cannot put the last piece into place

[Dadelus]

The only mosaic puzzle glitch I am aware of is if you completed the puzzle before getting the final piece from the dragon, then the puzzle can never be solved as the last piece won't go into place. Nothing happens when clicking on the puzzle to finish it. You must have the final piece in inventory when doing the puzzle.
About the only thing one can try is to load an earlier save and try again.