on reading your assembely code one thing is clear that you are initialising LCD everytime. Also as Mr. Michael has said it seems that LCD is not initialised properly.

Try to follow the start up procedure.

1) disable all interrupts (EA = 0; ofcourse this is state at poweron).
2) initialise all SFR registers necessary. (Timer related & interrupt related in this case)
3) now initialise ports if necessary.
4) now initialise peripherals (LCD in this case)
5) initialise global variables if any (mcount, ledtick, lcdtick)
6) now initialise SFR bits other than interrupt (TR0 in this case)
7) now set necessary interrupts using reg / bit address (ET0 & EA in your case)
8) let your timer isr only write the data (i.e. call only write_lcd_text from isr)
9) in case of lcd considor maintaining the cursor position.
10) try to follow structure as follows
11) ANY constant strings, write them at bottom of file(testing data)

REMEMBER THIS IS JUST A PATTERN NOT PROGRAM

ALSO THIS IS NOT THE ONLY PATTERN

...
/******hard ware definition here******/


here you have equ statements like
RS 	EQU P2.5
LCDDATE EQU P0

THESE ARE ONLY EXAMPLES


/*****MEMORY DEFINATIONS HERE*****/


here you have equ statements like
MCOUNT 	EQU 45H


/*****CONSTANT DEFINATIONS HERE****/

here you have equ statements like
OFF	EQU 0
ON	EQU 1
(IN YOUR CASE THIS DOESNOT EXIST)


/******NOW VECTOR ADDRESSES******/

ORG 0000H
SJMP START

ORG 000BH
SJMP TIMER0

change these SJMPS to AJMP or LJMP if necessary


/*****NOW ISR*****/

ORG 0030H  (THIS NO IS JUST A EXAMPLE. CHOOSE ANY NO ABOVE VECTOR TABLE

TIMER0:

MOV THO,#
MOV TLO,#

(BODY OF TIMER ISR)

RETI


/****ALL ISR ARE OVER NOW START WITH BODY****/
START:

initialise necessary sfr registers here
initialise sfr bits, global variables
initialise lcd

to initialise LCD

acall INIT_LCD
acall CLEAR_LCD

also get your cursor on row1,col1 position

now give a infinite loop

here: SJMP here

/*****NOW WRITE FUNCTIONS****/
INIT_LCD:

(BODY OF FUNCTION)

RET

similarly write other functions


when all functions ends

/****WRITE ARRAY OF CONSTANTS****/

MY_ARR DB 'A','B'.....

OR

ORG ####

DB 'A','B'.....

END

...