Text modifier animation glitch when editing a different run

Windows 10 app version 0.8.1268
This is a bit specific and hard to explain, but I'll try my best

I have a Text layer with 2 runs:
Run 1 = Never give up. Try again
Run 2 = →

1) I have a simple X position animation looping on Run 2 so that the arrow is bouncing to the right. I'm using a Text Modifier to target Run 2.
2) In a timeline, I changed Run 1 source text to something different.
3) The animation on Run 2 was not working anymore.
4) I go into the text modifier and it says it's assigned to Run 2 (→), but it's not animating.
5) I unassign and re-assign to Run 2 (→), now it animates as normal.

Hopefully that makes sense. Happy to provide any extra info if needed.