Hello all.
I believe I found a bug (((??))).
With Display Image Counter turned off, the image opens up as a separate page (not as an overlay) and an error is generated - Uncaught SyntaxError: Unexpected token }
I was able to pinpoint the error to includes/classes/zen_colorbox/options.php
For some reason the last empty echo is the one causing the error and the image to open in a separate window.

So replacing this

PHP Code:
echo 
',current:'
if (
ZEN_COLORBOX_COUNTER == 'true'
{
    echo 
'"{current} of {total}"'
}
else 
{
    echo 
''

with this

PHP Code:
echo 
',current:'
if (
ZEN_COLORBOX_COUNTER == 'true'
{
    echo 
'"{current} of {total}"'
}
else 
{
    echo 
'"Image {current}"'

solved the issue for me. The image overlay works now as it should and it displays the current image number only which is what I wanted.