Subcategory listing not proper in the category filter

I am using your DW Question Answer plugin for creating a forum, it works well, but some problem in Question page, the problem is in the Category filtering section.

I have some sub categories under the main categories, but I am getting a screen as shown in the screen shot once I selected a category having sub categories.

• http://prntscr.com/9mpxu1

Could you please help me to resolve the issue?