I've found the problem's source and I have suggest the solution.
1. Go to site's backend -> Extensions -> Template manager
2. Select JA Anion and press Edit
3. Edit parameter
Optimize Exclude and insert 2 rows:
jcomments-v2.1.js
ajax.js
4. Press Apply button.
This template has JavaScript optimizer (it allows to join all javascripts on page into one file to reduce number of http-queries). But it work not correctly with JComments' files. So we need to exclude the JComments' files from optimizing.