Duplicating mesh to speed up the model creation process, but sometimes Maya does not like that.
The mesh might skew while transforming, rotating or scaling, which can be very time to consume to fix and deform the mesh to an unfixable state.
This tends to happen due to Maya miss-calculation of grouping.
To fix this select the mesh that is skewing, then go into the outliner and move the node to the top-level removing it from any group.
This will fix the issue and the mesh will transform, rotate and scale normally.
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