My tabs cannot be deleted even though empty


I am new to Ragic and have followed the tutorial and also searched through the forum. I found some articles about deleting a tab, but it does not seem to work for me.

In the following screen capture, you can see that my tab “Test” is completely empty.

So as can be seen in the following screen capture, I right click on the “Test” tab and choose “delete”.

But nothing happens. No error message, no notification, nothing.
AND the “Test” tab is still there.

Does anyone know what is happening? Any solution?