What folder on the C drive do they get saved to? Is it also called My Pictures? If you created that My Pictures folder on your 1TB drive you used a poor name. The My Pictures entry is kind of reserved by Windows.
Okay, so let me ask a very basic question, because I'm not sitting at your computer.
Are the DNG photos that show this problem located on your C: drive? Go into Lightroom, and right-click on one of these problem DNG photos, and select "Show in Expolorer". Does a folder on the C: drive appear? Yes or No? (Note: don't tell me that you went into your operating system and found the photos on your 1T hard drive, that is irrelevant to my question, that is a waste of both of our time)
Problem solved. At the top of the import window, the "Select a Source: " bar includes four options: Copy as DNG, Copy, Move, Add. I had selected Copy as DNG. Now I know what that means. Lightroom copies the DNG files, puts them into a folder on the C: drive and sets the default folder to that location. I changed my selection to "Add" and the problem has been solved.
That particular menu bar is badly designed. I would have moved the "Select a source" to the right, and put Add first. I would assume that is what most people would want to do.
In any case, this has been a frustrating way to learn the ins and outs of Lightroom CC.
I appreciate all those who replied. thank you.
I have to say that menu bar has been the same for many, if not all, versions of LR. It also give you a description of what each option does, IIRC.
You have all the options you need, "Copy as DNG" (What that does is take whatever file extension you are using, even a DNG file, and converts it to a DNG, Yes even if the original is a DNG), "Copy" (I hope you know what that does. COPIES the files from the original location to another location of your choosing), "Move" (MOVES the file/files from the original location and places it/them in a folder of your choosing) all the above also put the images in the LR database and last but not least Add (All that does is add the images to your Lightroom database).
I always use the ADD option as I copy my images off the memory card to a folder or folders of my choosing first.