In qa-embed-layer.php go to line 52:
'image'=>array('(https*:\/\/[-\%_\/.a-zA-Z0-9]+\.(png|jpg|jpeg|gif|bmp))[^< ]*','<img src="$1" style="max-width:'.$w2.'px;max-height:'.$h2.'px" />','img'),
This is "parsing" the link to an image html tag.
As you can see there is no \+ sign in the regex. I am not 100 % sure, but just try to add it:
'image'=>array('(https*:\/\/[-\%_\/.a-zA-Z0-9\+]+\.(png|jpg|jpeg|gif|bmp))[^< ]*','<img src="$1" style="max-width:'.$w2.'px;max-height:'.$h2.'px" />','img'),
Does it work for you?