There are four references to function 'trimWords()' in the jquery.autocomplete.js code; three of them are "protected" by a check of 'options.multiple'; that is to say, 'trimWords()' is called only if 'options.multiple' is true.

This bug is caused by the 4th reference (actually the first in the source code), on line 185, which calls 'trimWords()' regardless of 'options.multiple':

$.each(trimWords($input.val()), function(i, value) {
	request(value, findValueCallback, findValueCallback);
});

The fix is VERY SIMPLE! Just add the check within the 'trimWords()' function as follows:

function trimWords(value) {
	if ( !value ) {
		return [""];
	}
	if ( !options.multiple ) {
		return [value];
	}
	...

Doing it this way allows the test to be removed from function 'lastWord()':

function lastWord(value) {
	var words = trimWords(value);
	return words[words.length - 1];
}

Without this fix, autocomplete consistently fails when the 'search()' method is used.