I have one mesh 10m*2m*20cm for example. When I check it's size in N-window it shows 20cm - here it's ok. But when I duplicate this mesh and rotate it on 90 degrees - mesh's size changes by itself! When I click again on the size line in N-menu it shows me not "20cm" but "20.000002cm". So the change is very small but still it's not normal. It doesn't happen all the time I work with the copy of the mesh and I can't actually find out when it happens. But i face this changing quite regularly.
Blender version 2.79. Is that ok? I wonder how I can avoid this bug.