Hi, thanks for your reply.
I have just checked and I confirm that what you say (X and Y coordinates switch to non-integer values after pasting or after moving the portion). In particular, It happens when I move my portion using the arrows. In fact, if I delete the decimals, the blur desappears and I can merge below without see any blur.
So I made the adjustment that you suggested (see in attachment) but it doesn't solve the issue. I also restarted the application, but nothing change.
As you can see in my attachment, I made a simple operation: I copied a rectangular from the background, I pasted it, and I merged below. The image is blurred (and the blur would be even more intense if I had merged another layer, as I often do). Note: this increasing does not take place with the command "Merge Visible" (alt + shift +cmd+ E).
Do you have other suggestions? Also, is it possible to define the offset value of the arrows? Do you think it could help?
Thank you!