This is a side-effect of the dual function of $highlight(): the identifier can be used in two ways
1) $highlight(text) - returns the item in Highlight list that matches "text"
2) $highlight(N) - where N is a number, returns the Nth item in the Highlight list, eg $highlight(3) returns the third item.
The reason $highlight(54564564532) returns "1" is the second function. When N is greater than 2^31-1, it is considered 0. So $highlight(54564564532) = $highlight(0) = the total number of items in Highlight list.