Using groups/outline, 1st row often reduces to zero height
 

I'm using Excel 2003, and am hierarchically grouping both rows and
columns into outlines. The summary rows/columns precedes their
associated grouped rows/columns.

Quite often, I find that after changing the depth of the outline
shown, row 1 reduces to zero height. I can drag it back down to a
nonzero height. Has anyone else experienced this? The text on my
column headings are upwardly oriented.