Custom style doesn't work for <p> tag?

Hi,

I've created a customstyles.xml file and a customstyles.css file.

In my customstyles.xml:

<?xml version="1.0" encoding="utf-8" ?>
<Styles>
   <Style name="Red word !" element="p">
      <Attribute name="class" value="RedWord" />
   </Style>
</Styles>

In customstyles.css:

.RedWord{color: #FF0000;}

When I select a paragraph in Fckeditor (for example, the first line I write) to apply my custom style "RedWord", it doesn't work.
However, if I select a head element (h2, h3...) and apply my custom style to it, it works fine.
And if I first change the paragraph to a head element, then apply my custom style to the head element, that works too: the element become a paragraph with "RedWord" class attribute.

If I change my customstyles.xml to this version (element "p" become "span"), that's work fine for all situations:

<?xml version="1.0" encoding="utf-8" ?>
<Styles>
   <Style name="Red word !" element="span">
      <Attribute name="class" value="RedWord" />
   </Style>
</Styles>

Why a custom style for a "p" element doesn't work on a default paragraph in editor?

Thanks by advance and excuse me for my simple English.

BR

Avairet