It's not a bug but documennted behavior. "When SET ANSI is set to OFF, the two strings are compared character for character until the end of the shorter string is reached". The empty value in the first record myVarCharField field will match any value specified on the right side of the "=" operator.

>CREATE CURSOR myCursor (myVarCharField V(10),myCharField C(10), MyRecno I)
>INSERT INTO myCursor (myVarCharField, myCharField, MyRecno) VALUES ("","",1)
>INSERT INTO myCursor (myVarCharField, myCharField, MyRecno) VALUES ("?","?",2)
>INSERT INTO myCursor (myVarCharField, myCharField, MyRecno) VALUES (" "," ",3)
>
>SELECT * FROM mycursor WHERE myVarCharField = "?"
>*-* Select record 1 and 2
>
>SELECT * FROM mycursor WHERE myCharField = "?"
>*-* Select record 2