jscalendar-icon not appearing (text-indent -1000em)

I've been battling trying to figure out why the icon to get the jscalendar pop-up wasn't appearing on any of my sites.

Eventually I started looking through the DOM of the page and noticed that the text-indent property for the pop-up button in the form had a property of textindent: -1000em.

Adding:

.jscalendar-icon {
  text-indent: 0;
}

to my theme's style sheet corrected the problem, so I went looking for the source of it and found it in jstools/jscalendar/jscalendar.css, where it for some reason sets text-indent: -1000em;

Is there some reason this is set this way in the original css file?

If not, I suggest removing that line.