When grouping data items together, the top level summary item is hidden from 
view when the outline is collapsed.  To reproduce, type some random entries into 
the same column and group them together.  When clicking on the "-" sign in the 
left hand toolbar to roll up or collapse the grouped items, the top item 
disappears.

In general, an outline should show a top level or summary item for each level as 
appropriate.  For instance, if an outline has elements 2, 2.1, 2.2, and 2.3, and 
the outline is collapsed up one level, item 2 should be left over as being 
displayed.

EXAMPLE

Before grouping:  

2
2.1
2.2
2.3

After grouping:

(-) 2
 |  2.1
 |  2.2
 |  2.3

After pressing "-" to roll up or collapse data, the following is displayed in 
OOo:

(+) [nothing is displayed]

What should be displayed:

(+) 2

See Microsoft Excel's implementation of the outline feature for further 
examples.