Disk not ejected properly
After I eject and disconnect an external drive or a pen drive in my Mac mini running High Sierra, the majority or times appears the following message:
DISK NOT EJECTED PROPERLY
EJECT (DRIVE NAME) BEFORE DISCONNECTING OR TURNING IT OFF.
I never disconnect it before I eject it , but even doing that, the message appears.
What am I doing wrong? Or it's a system bug?
Mac mini, macOS 10.13