DOCBOOK-APPS: empty cells in tables

Hello,

If I have empty cells in my tables - the resulting fo file seems to be 
invalid, since I get the FOP-Error:

"WARNING: Number of cell columns under table-row not equal to number of 
table-columns"

The same behaviour occurs when I start my cells on a different column than 
the first.
The work-around is simple: just filling up the missing cells with entries 
containing an empty Paragraph
(<entry><para/></entry>).

Is this a bug or am I (or is FOP processing) wrong?

Ciao
   jENs