Problem with word search

[Burkhard Schultheis]

I searched in Google groups in this group for my problem and found an 
old discussion from 2007 for my problem, but it does not answer my 
question because the discussion was inconsistent:
Someone stated that "word-search-forward machine" does _not_ find 
"running_machine_state". But another one stated it would (and should) 
find the longer "word". And this is the case with my emacs 21.3.1 (it's 
a development server where I cannot install the newest version).

How can I change this behavior? Or is it OK in Version 21? Or how should 
I search for a word? I've tried the regular expression \bmachine\b and 
it does find "running_machine_state" too! I think, this is the problem, 
but why? And how can I change it?

Thanks in advance!

Regards
Burkhard