Thank you for all your responses. It's good to know that I am not alone in this.
Something far worse happened to me recently with the Photos app. I noticed in System Preferences > iCloud > Photos, there was an option to "Delete and Disable" iCloud Photo Library (hereinafter "IPL") completely. It sounded to me like this would delete all of my photos from IPL so that I could get a clean start and retry the upload from my pristine Photos app library.
Lo and behold, when I did that, IPL somehow sent a signal to Photos that all of my photos needed to be downloaded, so it duplicated literally thousands of photos in a library that I had carefully pruned in Aperture throughout the years. Not only that, but it deleted half of my library! It went from 130 GB to 62 GB in a matter of minutes with no warning, confirmation, or even an informational dialog box. What a disaster this iCloud Photo Library has proven to be.
Thank God, I have a good backup plan and everything can be restored, but I've learned my lesson and have come to the following conclusions:
1. iCloud Photo Library is a disaster in its current state. This beta is not ready for public testing.
2. The best way (at least for me) to use Photos app now, is to turn off iCloud Photo Library, but keep the option for the Photo Stream on. That option automatically feeds all new photos from my iOS devices into Photos, which is almost perfect. Unfortunately, Photo Stream does not support videos, however. So, for videos, I simply connect my iPhone and Photos app does a good job of recognizing all of the new videos that need to be imported. With this setup, I can benefit from the Photos app, get all of my new photos and videos imported, and avoid the hassle that is known as the iCloud Photo Library.
I hope this experience helps someone in the future.