Yes, we are working to resolve this. In the meantime, you can hold down the key of the vowel that you want to make a tone on and select from the options in the pop-up box. Alternatively you can add the Czech language to your keyboard options and easily toggle between that and English. When you're in the App, select that one and you'll then be able to make all of the proper tone marks. This will resolve the issue for the time being.