Found the answer/solution to my own question and assume that some other folks might want to know too.
A $10 cable from Amazon, called "Dual Micros USB/Mini USB Cable has a standard USB 2.0male plug and branches to one mini and one micro male USB plug.
Now I have just run the cable through some tests and find that it is not perfect.
I works just fine if plugged directly into the PC's USB port, but slows down to below USB 2.0 specs if plugged into a USB extension cable. This doesn't happen with the cable that came packaged together with my phone. It continues to work just fine when plugged into the very same extension cable.
So the conclusion has to be that this new cable I bought is only marginally 2.0 compliant, and the moment any added resistence is added toi the circuit, it underperforms.