Listbox1.items.delete[1] Problem

[trolojik2]

at first my project is client chat project.

listbox1 contains nick names
on a user connect server listbox1 add nick on lines with listbox1.items.add(nick);
when a user disconnected or quited item deletes automaticly in this way > listbox1.items.delete(listbox1.items.indexof(nick) );

i will not click any nick (item)
when im looking nick list with listbox's scroll it this time if a user quits or disconnected
scroll going start of listbox1
I dont want to change scroll pos when a user quited