How to reproduce it
1. Create a new Impress file, insert the paragraph on slide and 
   select that paragraph

2. Choose Format ->Paragraph and select Tabs.

3. Input position (4cm), select the type (left)

4. Select (like Character) at the bottom of "Fill character" field and enter 
   character in textbox, like "test";

5. Click [New], click [OK]

6. try Tab stop on the paragraph

7. Click any other area on the slide except the textbox


Result
Tab characters or lines don't show before the paragraph.


Exceptation
Tab characters or lines show before the paragraph

Note
But if select paragraph again, Tabs can show once more.

Regards
Li Meiying