Steps to produce: 1) Insert USB flash drive. 2) Mount drive by clicking its icon in the side-pane (I don't use automount) 3) Suspend computer. 4) Remove flash drive. 5) Revive computer. 6) Thunar still thinks the flash drive is mounted and wont let me eject it. Obviously, this isn't the way you are "supposed" to use a flash drive, but I feel like Thunar should be able to figure out if the device is no longer connected, especially if I click refresh. Maybe the refresh function can include a quick "ping" of the mounted devices?
Actually, you might need to actually edit a file on the flash drive before suspending to get problems.
If you remove the flash drive before unmounting it, then you risk data loss, so you shouldn't do it.