Background: I have Thunar 1.6.3 but my system is a bit mixed up ... Openbox session running on parts of Lubuntu and Xubuntu. I'm mentioning this because it's possible that what I'm seeing is an artifact of my system and not the "norm".
I have a 500GB USB mounted.
When I right-click on the device in Thunar's side-panel and choose Unmount, I see a very, very brief flash of what appears to be notification pop-up.
To catch it, I mounted the device again and followed the procedure described here: http://askubuntu.com/a/352200 . So I opened a terminal window and pasted the following code:
Then, on unmounting, the screen showed this:
dbus-monitor "interface='org.freedesktop.Notifications'" | \
grep --line-buffered "member=Notify\|string"
Can a Thunar user please comment?
[04:14 PM] ~ $ dbus-monitor "interface='org.freedesktop.Notifications'" | \
> grep --line-buffered "member=Notify\|string"
method call sender=:1.26 -> dest=:1.35 serial=67 path=/org/freedesktop/Notifications; interface=org.freedesktop.Notifications; member=Notify
string "Writing data to device"
string "There is data that needs to be written to the device "TOSHIBA EXT" before it can be removed. Please do not remove the media or disconnect the drive"
[04:43 PM] ~ $