Broken: (example: 2.74 000dfc0)
Short description of error
When mirroring in Object Mode, either by using the mirror operator or by scaling, the result is sometimes wrong.
But when the object is mirrored by parenting it to an empty, which is then scaled and the transformation is applied (so the empty can be deleted), the result is right.
Exact steps for others to reproduce the error
Select both arrows. (Make sure not to move to move the 3D-Cursor, which is centered and serves as pivot center)
Press Ctrl+M to mirror, select the 'X'-Axis.
Now the arrows are pointing in different directions.
Add an empty. Parent both arrows to the empty.
Select (only) the empty. Press Ctrl+M to mirror, select the 'X'-Axis.
Press Ctrl+A to apply the empty's transform, select 'Scale'. Now delete the empty.
Now the arrows are pointing in the same direction. Which I had expected for the mirror operator as well.