That is weird.
64-bit Windows 8 Pro here. Tried to replicate.
Spine Editor decided to freeze up instead. lol
Then I tried again. Discovered a bug(?) where if you drag an image from the image list too fast into the viewport, the new slot and attachment doesn't get generated.
No JDK banner image though.
But I uninstalled JDK from my machine when I left my Java days behind me. Doesn't make sense either way.