Preserving smoothing group info for SMDS

[Jasper]

I'm having a strange issue here;

If I attach a new object to any editable mesh within 3dsMax, even if it retains smoothing data, and then export that as an SMD, the data is lost.

So for example, we have an SMD that's been imported here in max;



Note the smoothing data for the arms and weapon is present. Now if we compile it for source, here is the result in the model viewer (and in-game);



What's interesting is that the smoothing data for the custom object (in this case, the machine gun) is preserved, but the smoothing data for the arms is lost.

Here's my current stack;



I've read somewhere that SMDS do not preserve smoothing data, but rather 'normal' data, so I have a subtle feeling that the issue may not be smoothing groups, but rather all the verts on the arm are breaking somehow.

Anyone able to shed some light on this, particularly workarounds for the 3dsmax environment.

EDIT: Have checked and I believe it's definitely smoothing groups and not broken verts; adding a smooth modifier to the stack fixes the issue but the smooth modifier is not very discrete since you can't manually modify the groups of specific faces. It only accepts a global angle to smooth all faces, but I'd rather try and preserve the pre-defined groups for better appearance.