Comment 9 for bug 1084236

I'm not an expert but I've spent some time looking at the code for file formats in Pinta. What seems to happen with every type of image is that it is imported into memory and then exported, in effect creating a whole new image. Extra information like metadata gets lost along the way (for PNG, JPEG, and any other format).

The technology used underneath is from GTK, the GDK (drawing layer of GTK) and GdkPixbuf.
https://developer.gnome.org/gdk-pixbuf/unstable/gdk-pixbuf-The-GdkPixbuf-Structure.html
If I'm reading the documentation right GdkPixbuf only reads a very limited bit of metadata, enough to check the image orientation. The advantage of GdkPixbuf is that it is (relatively) simple, which is also the disadvantage. To avoid losing metadata such as Exif or XMP the code would need to get more complicated.

As a workaround you might be able using external tools to copy the exif from your original image to new image created by Pinta.