NAs in the response variable

I fitted a mixed linear model with ASREML-R, and I have missing data in both response variable (Y) and in one factor (X). For data in only one environment (none spatial data) I used the options na.method.Y="omit" to exclude observations with NAs.
na.method.Y="omit" did not work out, and give exacty the same fit than na.method.Y="include". So I tried na.method.Y="exclude" which gave a different result, and seemed to work well. The option given in ASREML-R pdf for exluding NAs in Y is "omit" (and not "exclude"). Was the term "omit" written erroneously in the pdf manual instead of "exclude" perhaps?
If not, what can lead to the situation "omit" option worked exactly as "include" in the presence of NAs in Y?

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SAIDOU Abdoul-Aziz
PhD student SupAgro-Montpellier/University of Niamey
UMR DIAPC, IRD Montpellier Center
911, Avenue Agropolis BP 64501 34394 Montpellier FRANCE

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Received on Fri Oct 15 2009 - 18:17:24 EST