USB flash key disconnect failure

I’m running OSX and my usb flash key just will not disconnect. Each
time I try it reappears a second later. In the disk utilities application the
same thing happens although the trace console says that the
disconnection has succeded. If I remove it swiftly before the icon comes
back on the screen there is no error message. However if I try
reconnecting the key OS X will not recognize it. I have to reboot to
achieve this. Many thanks for any advice.