I can reproduce the exact same behavior with the Imperial component in an empty Metric File.
New Project, Template <none>, Metric. etc.
So it's not just some faulty component.
Try again, start from scratch Metric
place Imperial TV
draw the line
rotate with copy of line and TV.
Edit Family, make Workplane based, load into project, overwrite.
Rotate with copy of the original line and TV, see the difference.
Edit Family, uncheck Always Vertical and load into project, overwrite
Rotate with copy again of the original line and TV, and observe the difference again.
Did it in empty Imperial Template (New project, Template <none>, Imperial etc.
and got the exact same result. Things may be set differently in whatever Template you chose to start from, but if you start from scratch, you should be able to reproduce the bug.
Make sure you don't have the Edited Family open when you try to reproduce this in a different project because Edit Family will take you to the open Family which you may have already changed and could cause confusion.