I asked Jose about this awhile back on the developer list; looks like I 
forgot to forward the answer. In brief:

IMHO it is a feature. When a document is updated, the old one is marked 
as deleted. So, after a search, the result is removed. The bug is in the 
dump routine.

Jose

Roman Chyla wrote on 9/13/04 1:51 AM:

> Hello,
> 
> could I open one old question? - it is about incremental indexing
> 
> On Tue, Jul 27, 2004 at 06:10:28AM -0700, Peter Karman wrote:
> 
>>I indexed a file with the word 'foo' in it. I searched for 'foo' and got
>>that doc. Then I removed the word 'foo' from the doc and re-indexed,
>>adding the -u option. Now a search for 'foo' does not return that doc.
> 
> 
> 
> Bill Mosely replied
> 
>>Interesting. That's either a bug or a feature Jose put in that I didn't
> 
> see.
> 
> the whole discussion can be found here
> http://swish-e.org/Discussion/archive/2004-07/7936.html
> 
> 
> roman
> 

-- 
Peter Karman  651-605-9009  karman@cray.com