I saw this event before when updating my HTPC to V11.0. I made a test system on a 16gb Sandisk usb stick 11-30 nightly build generic/ legacy. I plugged in another usb (fat32) stick with my mp3 files and the system does not issue a notice but does report safely removed message when removed. This is probably related to the HD problems with NTFS drives from last year. Pretty easy to duplicate with two usb drives. I tried to get a log file to share but get "Failed to paste log files." I might try a later build and see if the condition continues.
One other thing I ran across is file naming difference Linux/Windows. A few of my Linux mp3 filenames had illegal filename characters and causes some headaches trying to move/copy from LE to USB drives. So far these three showed up "(" ")" and "'"