This is not my normal workflow as I do not use Lightroom very much, but I did what you suggested. I opened LR (CC, version 7.5), imported a folder of raw images, clicked on one and used the transfer functionality to open that image in PhotoLab (1.2.2, build 81) and only the proper image opened up.
I tried this again this morning, but again everything worked properly on my machine. Perhaps you might think about uninstalling and reinstalling the components involved. If it were me I would uninstall and reinstall both Lightroom and PhotoLab, although I do not know if that would fix the issue.