acegen – Negative Jacobian for small finite element in AceFEM

I want to make simulation for 1 hexahedral finite element of dimensions 1mm x 1mm x 1mm. I need to use SI units (metres) as below in the code

<< AceFEM`;
H = 0.001; 

  "imp", {"ML:", "SE", "D3", "H1", "DF", "HY", "H1", 
   "D", {{"NeoHooke", "WA"}}}, {"E *" -> 20000 }];
  "H1", {1, 1, 
   1}, {{{{0, 0, 0}, {H, 0, 0}}, {{0, H, 0}, {H, H, 0}}}, {{{0, 0, 
      H}, {H, 0, H}}, {{0, H, H}, {H, H, H}}}}];

Why do I obtain the following warning?
WARNING: Negative Jacobian: 1.*10^-9 Possible clockwise (incorrect!) direction of master mesh. See also: SMTAddMesh.

What can I do to simulate the element without changing its dimensions?

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