The bug

While I was working on player rotation detection, I noticed that when I used the command "/testfor @p[ry=13,rym=9]" While facing ry=14 (according to the F3 info "Facing: south (Towards positive Z) (14.0 / 0.3)") the player was detected, and should not have been.

How to reproduce

1. Run:

   /scoreboard objectives add facing dummy
   /scoreboard objectives setdisplay sidebar facing
   /scoreboard players add @s facing 0

2. Face at: (Towards positive Z) (14.0 / 0.3) (/tp @s ~ ~ ~ 14.0 0.3)
3. Run:

    /execute at @a[y_rotation=13..9] run scoreboard players set @p facing 1
   

   → See how your score will change from 0 to 1.