.o or o. or o instead of .o. causes words to be shown unknown

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What steps will reproduce the problem?

foma file reads in lexc files like:
define Grammar7  Filter1               .o. 
                Lexicon7               .o.                
                CleanupEndings        .o.
                HarmRuleAAA           .o. <--- if instead of .o. there is .o 
               ...
                HarmRuleszorelolmely      .o.
                Cleanup;         
one after the other.

If in one such set there is .o or o. or o instead of .o., then the effect is:
No error or warning, but every word of this lexc file is reported unknown, like:
apply up> ballag
???
apply up>

What is the expected output? What do you see instead?
It would be very nice, it this kind of error were reported at compilation time. 
It took me several hours the find out the source of the problem now.

Original issue reported on code.google.com by eleonor...@gmx.net on 13 Mar 2012 at 6:02