Hi,
Thank you for letting us know about this issue. Regrettably, this seems to be a bug in the current version. I'm very sorry for this inconvenience. We will try fix it in the nearest version or in the next hotfix package for this particular Kentico
CMS version.
The workaround is not to browse the site in another tab while logged into the CMS Desk within the same browser instance or clearing cookies in the browser.
Best regards,
Juraj Ondrus