This is an unusual one. When I paste an image copied to the buffer with the print screen key, I just get a fully transparent screen, but the dimensions are correct.

Here is a gif

I draw a smiley face, then copy it. Create a new document (you can see that the new document's size is 32x32, the size of the face.) I paste the face. Then I press printscreen. I create another new document. (You can see the dimensions are now 1920x1080, my monitor's size.) I press printscreen on the new document dialog as well. I paste. It's just blank. Then I click Aseprite v.0.9.5, create a new document and paste it there successfully.

The last version I can paste a printscreen in (that I have) is 1.1.4.1. I have a gif of me trying the same paste in 1.1.4.1, 1.1.5, 1.1.5.1, and 1.1.5.2 I can send if needed, but it ended up being nearly 4MB. Regardless, only 1.1.4.1 works.

Just for clarity reproduction steps for me are simply:

1. Press print screen (or alt+print screen)
2. Paste.

A selection will be created of the right size, but with fully transparent pixels.
Aseprite 1.1.5.X on Windows Vista 32bit.