No object styles are applied in this example.
Expectation: When adjusting the length of a line, it's position should remain unchanged.
What happens:
When I adjust the length of a stroked line by entering a new width in the Length property, its Y position decreases by 0.5pt/equivalent.
When I adjust the x position by nudging with the Right or Left Arrow key, both the y position decreases by 0.5pt.
If the stroked line is grouped and aligned to other objects, the y position of the line decreases by 0.5pt regardless of its position/alignment within the group.
Adjusting the line weight causes y position movement also.

Currently using InDesign 17.4 on macOS Ventura but this has been my experience with earlier versions since around 2021, and updating the OS has had no effect.