Problem with user exit for CJ20N uisng EXIT_SAPLMLSP_030

hello all,

i am using FM = EXIT_SAPLMLSP_030 ( exit = INCLUDE ZXMLUU16 ),

here i have written code to prevent user from entering duplicate services in CJ20n,

if sy-tcode EQ 'ZSESTIMATE'  or sy-tcode EQ 'CJ20N'.  FIELD-SYMBOLS : <fs1> type ANY.    ASSIGN ('(SAPLMLSP)IX_ESLL[]') to <fs1>.     if <fs1> is ASSIGNED.       "required condition   endif.
 endif.

however the issue is when the select a service and tries to delete by selecting -ve symbol in the above screen shot,

the same is not updated (i.e no deletion flag is set)  in ASSIGN ('(SAPLMLSP)IX_ESLL[]') to<fs1>.

how do i catch this, do i need to use any other structure instead of IX_ESLL..

thanks in advance..

  ASSIGN (