1 Create a new Impress doc
2 Apply "Title Slide" layout for the slide, then enter some characters in the
Title box and Text box
3 New a slide page, apply "Title, Text" layout for the slide, then enter some
characters in the Title box and Outline box 
4 Switch to Outline view, click "First level" on Outline bar

Result
In DEV300m49, Outline paragraphs hides in the Slide with  "Title, Text" layout.
But Text paragraphs don't.
but in OOo2.4.1, all of paragraphs in the slide hide.