When you’re writing a large pose and moving around in it with the arrow keys, the cursor sometimes jumps to the top line in response to pressing the down arrow on the bottom line.
This issue is minor! But, it happened to me a couple times, and I was confused enough I decided to dig into how it happened.
This only happens when you have a large enough pose that the text entry box has a scrollbar. (It’s easiest to make this happen if you open some of the side-panes.)
Then, press the down arrow on the bottom line. On the right-hand half of it (as measured by characters, not space in the field), the cursor will jump to the end of the line, which is expected… but on the left-hand half, the cursor will instead jump to the same horizontal position on the top line.