Why is this happen ?

You are trying to write the character before you have stored it in CGRAM and you are overwriting the first CGRAM character with the second one. Try this:

start: 
    lcall INIT_LCD 
    ... 
    ; CG char 0
    mov   a,#40h ; write to CGRAM 
    lcall WRCommand2LCD 
    MOV   A,#04H 
    LCALL WRChar2LCD ; write row 0 
    MOV   A,#00H 
    LCALL WRChar2LCD ; write row 1 
    MOV   A,#04H 
    LCALL WRChar2LCD ; write row 2 
    MOV   A,#04H 
    LCALL WRChar2LCD ; write row 3 
    MOV   A,#08H 
    LCALL WRChar2LCD ; write row 4 
    MOV   A,#11h 
    LCALL WRChar2LCD ; write row 5 
    MOV   A,#11H 
    LCALL WRChar2LCD ; write row 6 
    MOV   A,#0eH 
    LCALL WRChar2LCD ; write row 7 

    ; CG char 1
    MOV   a,#48h ; write CGRAM  ; These 2 lines are optional.
    lcall WRCommand2LCD         ; CGRAM addr will already be 48H.
    MOV   A,#04H 
    LCALL WRChar2LCD ; write row 0 
    MOV   A,#4H 
    LCALL WRChar2LCD ; write row 1 
    MOV   A,#4H 
    LCALL WRChar2LCD ; write row 2 
    MOV   A,#4H 
    LCALL WRChar2LCD ; write row 3 
    MOV   A,#4H 
    LCALL WRChar2LCD ; write row 4 
    MOV   A,#4H 
    LCALL WRChar2LCD ; write row 5 
    MOV   A,#4H 
    LCALL WRChar2LCD ; write row 6 
    MOV   A,#00H 
    LCALL WRChar2LCD ; write row 7 

    mov   a,#80h ; go to address 0 
    lcall WRCommand2LCD 
    MOV   A,#00H ; Write character 0 
    LCALL WRChar2LCD 

    MOV   a,#81h ; go to address 1 
    lcall WRCommand2LCD 
    MOV   A,#01H ; write character 1 
    LCALL WRChar2LCD