Tab container Issue after updating AjaxControlToolkit to 16.1

Hy 

After updating the AjaxControlToolkit to 16.1, I have an issue with TabContainer.

Each tab I visit, has a CssClass attached to it: ajax__tab_xp .ajax__tab_disabled .ajax__tab_tab and it is never removed. This is an issue because we have specific styles for disabled tabs. (Asp.Net WebForms)

Here is a sample project that shows the issue: https://we.tl/EeDOKGhazv 

Thank you