Merge books keeps popping up

Hello,

This is an issue I have EVERY single time I use Calibre :
I am editing something (title, series, etc.) and then clic on another line and get the merge books dialog popup.:rolleyes:
This is very anoying and I don't know how to prevent that.
I know that this dialog is supposed to pop up when you drag a book on another, but I am not doing that!
Anyway I have never had to "merge" books (in what situation would you do that?), so : is there a way to just disable this behavior? :)

Thank you for your help
Emphyrio