Please see that both listname and Listname1 are text strings that match yet they are giving different results with categoryfind(). I am sure I am missing something, but I cannot determine what.
What you created was testing and testing1 exactly the same, but if you create testing with the fopen loop and testing1 with equaling string then you get those results i posted.
By the way, on my system the watchlist names, using the Amibroker UI to modify them are truncated at 40 chars, so be careful if you create names outside of the application (the first one in your example is longer).