It's not a bug but documented behavior. See String comparison in VFP

>Some old code I maintain, behaves differently in VFP9SP2 than in earlier versions. I know that this code is not recommended, but I didn't write it...! Try the following:

>Select * from yourtable where upper(alltrim(yourfield))='A'

>Note that VFP9SP2 will also select all the records where yourfield is empty!!! This must be a bug?
>
>Update: Further investigation reveals that I get the same result in VFP8. This means that these two code segments behave differently

>Select * from yourtable where upper(alltrim(yourfield))='A'

Use yourtable
>Browse for upper(alltrim(yourfield))='A'

>In all cases I have Set exact OFF and Set ansi OFF.