Let's say you have two tabs in a Terminal window. One of the things with the bug is, if I tap on the left tab, it opens the right one. If I tap on the right tab, it opens the left tab.
Same problem in Xcode.
When I notice this bug, and if I try to rearrange the tabs by drag-and-drop, Xcode crashes.
It's kind of hard to explain but if you've seen it you know it.
Not sure how to replicate it, but more often than not this bug happens to me. I usually create tabs in Terminal using Cmd-T.