In build 819 I tried using the "Re-order strings" feature. It moved the String, "0: None," to the wrong position. I upgraded to build 842 hoping it would fix itself. I noticed that it would not let me change the 'next string' to "0: None." Instead, it would use the last string instead of "0: None." That string eventually leads to the string that causes this bug.
I upgraded to 846, and tried moving "0: None" to the correct position (the top). It would not let me move "0: None." I tried moving the others so that "0: None" would be at the top. When I pressed the top up button, it moved "0: None" to the top and created an exact duplicate of the selected string. 😮dd: I deleted one of the duplicates, and it moved "0: None" back to the wrong position. I pressed the top up button again, and changed the "next string" of some string to the duplicate string and it disappeared.
I don't remember very many details. This is a very odd and complex group of bugs. I'm sure I didn't get the story exactly right. 😕