A picture follows my mouse as if I pressed the left button all the time while exporting

I just got it for the second time that I select a picture with the mouse but what ever I do, I can get rid of it anymore. I can deselect it, select it and further pictures, but it keeps following my mouse even after coming back when having switched to another application.
I can use picasa normally (selecting pictures, selecting another folder, etc...) and I can use other applications. But within Picasa this picture keeps following my mouse and pictures keep evading my mouse to make space for the picture following my mouse. But click doesn't put it into that or any other location.
When selecting another picture in order to move it, I can do that and during the process of moving it in the library the first picture stays where it is. As soon as I drop the second picture somewhere, the first picture is back at the mouse pointer.
This time I selected a picture and had a group of picture in hold just being exported. When asked whether I wanted to stop holding them on clicking the new picture I declined, because I didn't want to interfere with the exporting process. Now, when I switch back to Picasa I have this picture moving with my mouse pointer.
After the export was over the picture following my mouse disappeared. The last time I had to restart Picasa to make it disappear. (at least, as far as I remember)