Because it seems to be an issue with jComments not the template.
Standard template - no issue with JComments.
Other templates - no issue with JComments.
JoomlaShack template - issue with JComments.
Conclusion: the fault is with JComments.
Lovely logic skills, pal!
You know, if I had more then a picture, but the link to your Web site, I could trace the problem precisely and prove to you that the JComments are not at fault. But you seem to know better so good luck figuring this one out.