This may or may not correlate to the specifics of the problem with the mouse-over display event, but I had a similar situation using a free script to place a function on a page.
I think in some situations as the free-script will come with a demo string, say "ACGCCT1729ct" = sum of 12 alpha-numeric characterts..." you can SUBSTITUTE
a custom text string as long as you keep the string INDEX exctly as is coded and use the same size of the index, namely 12 characters (for this example here).
Otherwise, It will have a 'bug' and not function as exepected (but not always depending upon the author's strictness of the index.) So try to make your custom message 'co-indicial it stiring-length magnitude' and see if it will go. Hope this help.