Meanwhile I have an idea why it is not selectable.

In some of the cells of the first row I rotated the text by 90deg.
Because of this the first row gets a specific height in Table Properties (which should not be altered).
Because of this I cannot disable "allow row to break across pages" for the first row.
Because of this there is a mix of Specific Heights and undefined heights for the remaining rows.
Because of this the table cannot be treated as one object and the row split defined once for all.

Meanwhile I disabled for all but the first row individually the row split. It works now but I have only 20 rows.

Users with 300 rows will a problem here.

Can you confirm this?

Is there a way to define a default value in Word2007 for all (future) tables?