Hi i have found that the invisible feature of Area Style/Filling in Table 
Properties has some problem. It is not working when following steps are 
performed:

1. Create a presentation in Impress.
2. Insert a table in that presentation.
3. Select four adjacent cells (2 in rows and 2 in column) such that they form a 
square or rectangle.
4. Merge the four cells.
5. Then select the merged cell and split it into 3 cells from the split cells 
option.
6. Then click or select the bottom right cell of the splitted cells.
7. Click on the invisible field of the left combo box of Area Style/Filling in 
table properties.

You will find that the selected cell would not become invisible.

I think that there is some problem in the "Split Cells" functionality which 
results in the failure of the functionality of the "Invisible" for some cells.

Configuration:
Intel Pentium Core2Duo 2.0 Ghz
4096 Mbs Memory
Operating System: Microsoft Windows Vista
NVIDIA GeForce 8400M GS Graphics Card
OpenOffice 3.0.1
OOO300m15 (Build:9379)