There's a thread about this on chesstempo (link). Here's Richard's reply to a similar problem:
Hi dvdbly,
As a gold member, you can see your problem mistakes on your stats page, you played 3.Qd7 here, instead of your intended 3.Qd8, so it looks like it is probably a mouse slip. The most common cause of mouse slips (after accidentally letting your finger off the mouse button too early), is not realising that the drop target of the piece is your mouse pointer, instead of the center of the piece, so if you drag the mouse from the very corner of the piece it is possible that the mouse pointer will be in an adjacent square, while most of the piece is another square when you drop it. It is likely that this is what has happened in this case. If you haven't done so already, I suggest you turn on the highlight drop square option in your preferences, as it will give you visible feedback on the square that you will be dropping the piece if you let go of it at any particular instance.
Regards,
Richard.
Richard can check your records as well, to see what move you made.
i dont mean that on verry verry seldom occasion alternatives are incorrect, but i think 5 time now i did the right move but it then says mistake and shows me exactly the move i made?? i mean i believe i could do the mistake to not realize my mouseslip ones.. but 5 times, i cant believe i hallucinated 5 times... did anyone else every experience that problem??