Please see Attachment.
It seems Ajax error.
How to disable ajax or fix this problem?
Please share your page url to check this.
http://lectus.kr/all-courses/
Thanks for sharing the site url. I can see when you click on different category then the courses are filtered according to your category.
I am not sure what your issue is then. The courses should be filtered and it is filtering the courses. So please share more information to clarify what the issue is.
I select another category, immediately show current contents.
but AJAX change previous category contents.
Sorry I can not speak English well.
Ok I guess I understood your query. You want your previous content also and new content also.
Then use the filter widget present just below the category widget, refer:
http://screencast-o-matic.com/watch/cDje6IiH2x
Let me know if this helps.