Hang when unmounting drive.

I'll have a drive which is mounted and all is well.
When I come to unmount the drive the screen appears to hang for maybe a minute or more (so the up/down arrows do nothing) then the interface will come back and all if well again, I can mount
a new drive.
If I eject the drive in windows it doesn't seem to change the hang at all. I assume some form of unmounting is going on in the background but it's hard to know what's happening when there's no feedback about what's going on.