Video frames in timeline not aligned to chosen FPS

I'm working on an animation in Photoshop. Currently, I have a small looping animation that I created for testing. The animation has six frames, and the FPS of my timeline is set to 12. This would indicate to me that I would always have exactly 12 frames in every second of the timeline, but this doesn't appear to be the case:

If you look closely, the "06f" marker is slightly after the video layer ends. This problem compounds itself when I attempt to loop the animation by duplicating the video layer within a group:

After 25 seconds of looping, the entire looping animation has phase shifted so that the middle of the animation falls on each second, instead of the animation ending at each second.

I'm trying to synchronize this animation to music, so the desync is very noticeable as the song progresses. I'm not sure what I'm doing wrong or why the frames aren't occurring as expected - can anyone help?

Let me know if I can provide any additional details!