Can not display bullet points in product description

[Selina]

I am using Joomla 2.5.4 and Virtuemart2.0.2 to create website. When I edit the product description using the "insert/remove bulleted list" button or I write the code in "HTML Source Editor" straight way, it displays the result as below

It is what I want. However, after pressing the save button, the ul and li tag will be changed to <p>. Please see the picture

Would appreciate for any help!