I am trying to reproduce this but I cannot.
The UI of the mirror interface in your video is missin the ability to choose what kind of object is to be mirrored (Faces, body, component) . Mine looks like this:
Also I note that you are doing this with a linked component and the link is preserved after the mirror. That is most certainly the reason the mirror is failing, because mirroring a component requires to auto-edit and modify the original copy in the mirrored version. Linked components, however, are static.
When I try the same with a linked component, the correctly mirrored component is not linked.
Also, keeping purchased parts such as this switch linked is unnecessary. Unmodified purchased parts should not be linked components.
Maybe you could share your design so we can investigate this odd behavior.