I just experienced a situation of trying to move a folder into PB4. The folder contained just six files. In order to facilitate a move, I held down shift and control keys. To my surprise only the folder name appeared in PB4, no icon and no folder contents. More disturbing is the six folder files have disappeared completely from the hard drive. They do not even show up in the recycle bin.
At this point I don't know if this is a one-time occurrence but I will attempt to experiment later today to see if this can be repeated. Thankfully, I had just burned a CD of the folder contents in order to give to someone else. Otherwise I would've been SOL.
customized Desktop PC (Haswell i7 4770 3.4 gHz with 32 GB RAM), Windows 10 Pro 64-bit, 256 GB SSD, and a Microsoft Surface Pro 2017, Windows 10, 512 GB SSD, 16 GB ram, i7