I have no idea how I got into this situation, but it’s a strange one. In the following .gif, what I’m doing is simply pressing the left arrow key repeatedly.

Note the following:

• When the cursor reaches the start of the initial line, the next leftwards movement jumps up an incorrect number of lines (should go immediately above).
• In the gutter, the soft-wrap indicator dots (if that’s what they are?) and line-numbers are completely out-of-sync with the contents of the editor’s buffer. For example, if I attempt to click my cursor onto the word "Sorry" a couple of lines above the one labelled as line 23, the cursor jumps to the end of the line labelled as line 12.
• (Not shown in the gif) I can’t click my cursor into any of the text with a dot in the line’s gutter. Doing so results in the cursor jumping upwards to the nearest line with a number in it’s gutter.

I’ve had soft-wrap enabled by default for a good week or so now, and haven’t run into any problems until now. I have no idea what combination of things led my editor into this state.