I understand what you mean, I just can't see the same on my test site.
Can I get credentials for your site and see for myself? I will probably want to take a copy of your site for testing if that's okay.
I will mark your next reply as private so that I can get log-in credentials from you—you may want to create a temporary admin user for me to use that you can later delete. And be sure to have a current backup of your site, even though I don't intend to make any changes other than possibly to temporarily add a backup plugin to take a snapshot of the site.
Can you also confirm the url of where I can see the problem. Which page are you adding the tabs too?
I looked at the site and see that, yes, "active in" is added to all of the tab content panes.
But I see that the cell responsible for the tabs has its content generated by a custom shortcode.
I quickly added a cell for testing that adds the markup for the tabs directly to the cell and it worked as per my local test site, as expected.
I didn't see where you have defined your custom shortcode, but I suggest you either add the markup for the tabs and panes directly to a Visual Editor cell, or use a tabs cell to insert the tabs and panes into the layout.
After more testing I was finally able to consistently reproduce this, and I have escalated this thread so that the source of the problem can be identified and fixed by the developers.
I'll keep you posted when there is something to report.
You are right. Debugging a client site on Friday took down my computer and I had to perform a clean install, and that meant losing all of my existing test sites.
I must have selected smooth fade on the test I made last week but didn't on the new test site this week.
Thanks for pinpointing the problem.
I have passed that on to the developers, and am reverting this ticket to escalated.