The hover bug solved the problem of next/prev images (and “close” too), but not that of loading image.
So I solved this way:
1) downloaded from colorbox the original file colorbox.css (inside the css folder in the archive)
2) replaced the colorbox.css with the one of the theme I used in lightboxPlus
3) In my case (elegant theme) I had to adjust the alignment of the box corner always in the colorbox.css
