It IS definitely a bug in Windows. And if you look at the second screen shot I provided, there are two tabs under the printer name. One tab is for one driver (standard) and the other tab is for the other (duplex). Now, I'm quite sure that not too many people do what I have done, so there probably is not a lot of testing on this. But it is DEFINITELY a Windows problem.
What should be done (if anyone from Microsoft is listening), is fix the tab so it reflects the printer's name that is displayed in the printer list (say of Word, third screen shot). Secondly in the second screen shot you see the bold printer name "... (standard)" but right under it is the other printer name "... (duplex)".
Whoever programmed this never did the proper Q&A tests because this is glaring problem.
And as for why this is being done, I have documents that I want to print out that need to be duplexed. Some are on the long edge, some on the short edge and some not at all. But I don't want to open Word to print them out one at a time. I have a VB.net program that goes through and prints the documents out to the correct printer, with the correct duplexing, since I cannot address print options though the Word.Application object in VB.net (another issues that Microsoft needs to address).
So, what I have created does work. There is no driver conflict. But there most certainly an issue on how Windows is displaying and accessing each instance of the printer driver/properties.
If I can be of further assistance, please let me know.