Hey, thanks for supporting me :)
It's actually intentional, even though it looks a bit odd if you focus on it when it's not in motion. This is how the original pokemon sprites worked as well. They probably didnt use a flipped side frame because it would look nearly identical to the other and removing frames from an animation actually makes a difference on the Game Boy that had very limited space to work with.
Either way i'll try to add the flipped frame soon!