I am still not able to replicate the problem, I changed my browser language to Russian but it still works for me 4 times in a row editing.
We did change to a new version of CKeditor in version 18.104.22.168, if you still have the old one on disk from before the upgrade you can try switching back to a previous version from Web.config or try using TinyMCE to see if it makes a difference. You can look on disk to see what older versions of CKeditor you may have and point it to the old version by editing this setting in Web.config
<add key="CKEditor:BasePath" value="~/ClientScript/ckeditor42/" />
also see this thread and make sure you applied the needed change, it could be related except you say the problem happened for you on our demo site and it already has this update.