[R] Is this a bug or am I making a mistake?

[Walter Anderson]

I have a data frame that I am extracting some records from and noticed 
the following issue

I originally used tmp <- subset(dd, dd$EVYEAR==2012 & dd$EVMONTH=='02')

and noticed that I wasn't ending up with all of the records I should 
have; however, when I used

tmp <- dd[dd$EVYEAR==2012 & dd$EVMONTH=='02',]

I did get all of the records I should have.

I thought the two forms were equivalent, am I mistaken?