jQuery autocomplete: how can I remove one character from the inserted value when it doesn’t match?

Question

I am using "jquery.autocomplete.js"(Version 1.1). My autocomplete configuration is

multiple: true,
multipleSeparator: ",",
mustMatch: true,

In my search list "javascript" is a value.So when I am typing "javas" it is showing the "javascript" value but when I am typing "javab" it is removing the whole word.It is happening for the "mustMatch".But I want to remove the wrong inserted character(in this example only "b" not the full word "javab"). What is the solution for this? It is urgent please help...