clone stamp tool won't remain anchored.

Hi All,

I am using the clone stamp tool and used it for two months nearly every day.  Today the sample point began to follow my cursor even though it was anchored in the area where I wanted.  This has cut my productivity at least in half as I am constantly finding a new anchor point every one or two stamp clicks.

Now, don't ask me am I holding down as I paint with the clone stamp tool.  I know that under those circumstances the anchor point moves.  I'm using single click stamp actions and under those circumstances, the tool has always remained anchored at the original sample point.  Any clues anyone please? I've restarted, PS, restarted my laptop, checked for updates to PS, reset the crop tool and nothing has worked...