Generally speaking this does not seem to cause problems, but in tighter security environments where URLs must be correct it does. For example, one customer experiences a transparent calendar picker like the image attached to this case. The same customer provided a solution to this problem:

It is in theme.jsp. There is a line like this:

String path = request.getContextPath() + "/includes/js/calendar/skins/aqua/";

The path variable is then used in lines like this:

background: url("<%= path %>/normal-bg.gif");

Because there is a slash at the end of the path variable, and another one between the path reference and the file name you end up with the double slash. We edited theme.jsp and remove the trailing slash. After flushing the browser cache the date picker is now properly visible.