Sometimes skype failes at typing text in a chat window. Usually it happens after some chatting or sending files and closing all chat windows. Entering text with skype`s api not affected. Even if you can type nothing in a native skype`s windows, you are still able to do it with skype-to-pidgin plugin. I`ve got this bug while the plugin was active, inactive, uninstalled, so it`s skype`s fault.