When I enter text in the "Close image text" box on the Interface tab, it seems to be ignored. All I see is an X in a circle at the lower right-hand corner of each lightbox image. "Overlay close" and "ESC key close" are working fine.
Even better than text, if there were a way to specify that the X gets displayed in the UPPER right-hand corner, that would be very helpful. It would be consistent with most common UIs that users experience. People don't look for the X in the LOWER right-hand corner. I've had complaints that folks can't figure out how to close the lightbox, even though the X is right there at the lower right.
Here's all the system info from the Support tab: