The attached part pb1130411.prt fails when using File > Save As > Mirror Part with the option Mirror geometry with features due to Sketch 1 (#96, ID 91352), because it has extern references to assembly pb1m0046d320_scheletro_1400.
When redefining the Sketch and accept to unalign all extern references, the part can be mirrored with features.
And yes, this generates the features in their original location and then mirrors the geometry by the Mirrored Merge feature.
When using Model > Create in the assembly and selecting sub-type Mirror, the part will be created exactly the same (except for the mirror plane reference).
This is no surprise, as not all features can be mirrored as desired. For example a mirrored coordinate system would become left-handed (Anton called it a mirrored universe). If it doesn't, curve by equation would require all relations to be converted (which can be difficult, depending on what functions are used) - maybe even if it does, as only some axes are inverted.
Obviously mirroring geometry is a hundred times easier than mirroring logic (at least when assuming that both would be done appropriately). Not impossible, but very tricky!
