<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>
List index out of bounds (-1)
I was dragging tabs from left to right and the other way around.
When I dragged a tab to the right, above the session tabs and out of its inner boundary, then this error occurred. I attempted to release the dragged tab above the left-pointing arrow at the very right of the session tab group. The error popup appeared twice in a row for a single drag-and-release event.
The problem happens rarely. I cannot reproduce it.