I think the confusion over the naming conventions between V4 and M4 and subsequent instances of the same figures, is due to V4's name being Victoria4, while M4's actual name is Michael 4. 

Do you notice the difference? There is no space in V4's full name. 

So, if you load a 2nd instance of M4 into the scene, unless you change the name yourself it is going to automatically renumber Michael 4 to Michael 5, Michael 6, Michael 7, etc. Whereas with V4, because of the different naming convention used, it will add a space followed by the 1, 2, etc. IIRC, Poser's method of renumbering figures (or adding numbers to figures) has to do with how ERCs function and the old problems with eliminating cross talk in conformers.

So there is no need for a bug report as Poser is renumbering as intended. The fault here does lie with Daz's naming conventions not remaining consistent between the figures. They didn't even bother to change the name of Hiro 4 or Freak 4 in the cr2's, as loading them in with two M4's in the scene, Hiro's name will be Michael 6, and Freak's name will be Michael 7 (or the like, depending on what sequence they are loaded in). I can't know if the the same is true for Aiko 4's name remaining "Victoria4 #" or not as I don't have Aiko 4. (Been waiting for her and the kids 4 to go on sale like hiro and freak did, but never saw it happen and I'm not paying full price for figures that are so old).

 

As for the problem with the M4/K4 mixer (I do have the script, but not K4, so I can't test this myself), one solution may be to first transfer the rigging from the mixed figure to the shirt. In PP2014 you can do this by having the shirt body selected, then go to Figure > Copy Joint Zones From... and select your mixed M4/K4 figure. I would make sure that the full shape of the base figure the shirt was originally built for is dialed in first. So, for example - if the shirt is originally for M4, then have your mixed figure at full M4 scale, with zero% of K4's shape dialed in. Does this make sense? Hopefully I'm describing it correctly. If the shirt was originally built for K4, then have K4's shape at 100%. Once you do the joint zones transfer, you can then try conforming and scaling the figure. Again, don't know if it will work, but it's a theory. If I could test it myself I would.