I note the error as well, this only happens when using th meshing toolbox. As a workaround do the TET10 meshing using command "MESH > GEOMETRY > SOLIDS" and click in OPTIONS:
In the new form make sure to activate the option "MIDSIDE NODES IN SURFACE", this way the new created midside nodes will be located for sure following the curved surfaces:
In fact, the result will be something like this, the midside nodes follows perfectly the curved geometry:
You can play with the MESH SIZING in the meshing toolbox and dynamically change the mesh size in curves, no problem, but when you are happy with the mesh density prescribed in curves run the tet meshing command from "MESH > GEOMETRY > SOLIDS", click in OPTIONS and make sure to activate the parameters "Midside Nodes on Surfaces". Also I suggest to activate the option "Detailed Status Messages", this way you will have plenty of information from the tet mesher that has been improved a lot in the last versiones of FEMAP 11.1, now it creates tetrahedral elements with very good quality!!.
I am sure the FEMAP guys will take care of this error in the Meshing ToolBox and will be fixed in the next release of FEMAP V11.2.