Reproduction steps:
1. Open the attached file;
2. Open the scene "BugExample";
3. Click Holly -> Mesh -> Holly_Body and observe the mesh in the Scene window;
4. Click Holly_NoWeld -> Mesh -> Holly_Body and observe the mesh in the Scene window;

Actual result: the model with disabled "Weld Vertices" import option ("Holly_NoWeld") has the mesh which is split into two parts.
Expected result: the model with disabled "Weld Vertices" import option ("Holly_NoWeld") should have the single mesh.

Note: the mesh is split when the model is imported as .MA file, "Weld Vertices" import option is disabled and the mesh is created with more than 65k triangles. Everything looks fine with .FBX model or when the option "Weld Vertices" is enabled with .MA model.

Reproduced with: 5.6.0b1, 5.6.0b7

Could not be tested with older versions than 5.6.0b1, because the function "Weld Vertices" was created just in 5.6 beta versions.