Maxxx, I believe Roygee is correct here.  The Inset Faces button/function has been used as the tool for insetting polygon groups of faces in Blender, since 2.6.  While the original Inset Polygon addon was introduced in 2.63, it was never intended to create the inset type you're expecting from the 3dsmax Inset workflow.  It's a bit confusing, but Inset Polygon is not the tool to use for face groups, but the hotkey still works correctly because it's been seamlessly assigned to Inset Faces since Blender 2.6.  Unlike in 3dsmax, in Blender, there are two completely unique inset tools, which are intended for different objectives.

Aaaahhhh.  Now I get it.  Ok, I see now that these are actually two different tools here.  However, I think that the REGION function of the Inset Polygon is still broken, Lux.  Consider the fact that the tool is supposed to be used to create an inset region, not just on individal polygons, but also regions of selected faces.  I'm not sure the difference between that, and the Inset Faces tool, but it's definitely confusing here.  The extra edges are created even with "region" selection on, which can't be correct. I wasn't aware that the Inset Faces operation was the one actually associated with the "I" keyboard shortcut, but now I do see that.  However, the "region" function of the Inset Polygon tool is supposed to behave very similarly to that.  I'm not sure why it exists, if the inset faces option is actually the one which works the way we would expect in that case.  Just trying to figure out why that is, so that I can use the tools as properly as possible in my work.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.