Why video appears in lower left corner when offset is checked in strip transform parameters?

In my case I’m creating a movie with the resolution of 1080×1920 (9×16). I have footage that’s 1920×1080 (16×9). My idea was to scale it to fit the dimensions of the movie. I thought I could do it with Transform Effect Strip. But the problem is that I need to enable Image Offset first.

When I checked "Offset", the video took its own aspect ratio. Why did it appear in lower left corner?

After I try to change the offset a little bit (just to see what happens), video seems to move a bit and scale up for no reason.

Next, when i play the result, it is actually showing that scaling was not applied.

From this point I’m already confused. I’m stuck because if I add Transform Effect it is scaling my video with the pivot point located somewhere in the center of the preview area, scaling it like this will send my video far outside of the preview area (it makes it nearly impossible to adjust scale with precision). I expected the pivot point to be in the center of the video.

What are the solutions to this problem?

Is it a bug? I heard people are struggling with similar problems since 2016!