[Bug] Wrong keyword count if keyword string conains special char

I′m a spanish user of the plugin. When i use common letters in spanish language like ó, ú, í, á, ?, etc… into the keyword string then the page analysis tool shows wrong the number of times that the keyword was used because always show 0.

https://www.ads-software.com/plugins/wordpress-seo/

I′m using this plugin at my webpage https://www.vozidea.com and face this issue, i think that is a plugin bug and not an error on my side.