In some situations you would want to apply a single orientation replace on a larger area which can be accomplished by using symmetry to extend your build box size. If it also mirrors this you would get undesired results.
Right now if you replace a shape with a shape (non cubic), it takes over their orientation. Which makes it seem like it's mirroring the orientation although it doesn't. Which is why you can see it if you replace a shape with a different shape, then it uses the orientation selected in build mode for everywhere.
The 'fix' would be to add a "symmetry mirror" toggle in the **Remove/Replace** menu to disable/enable mirroring on symmetry planes.