When you use tags starting with umlauts, this plugin seems to have a problem to show the umlaut letter in the head of the tag index properly. For example, when you have an "Ö" the tag map will output "�".
Maybe something wrong with the character encoding in this plugin?
My site encoding is set to UTF-8, which normally doesn't have any problems with umlauts.
Would be nice if you could give a workaround for that or - even better - provide an update to fix this. :-)