The suggested patch answers bug report #2806232, see:
Description: When mounting something on a folder that is not listed in the static device list (/etc/fstab), Xfe 1.19.2 keeps using the regular "folder" icon. There is no visual indication that the folder is now a mount point. That is impractical when manually mounting stuff. For example, when manually mounting a USB stick on /mnt ("mount /dev/sda1 /mnt"), the same "folder" icon is used for /mnt before and afterwards. -- With the attached patch, Xfe looks at both the static (/etc/fstab) and the dynamic (/etc/mtab, or more precisely: /proc/mounts) device list when deciding which icon to show. With the patch, /mnt gets a different icon after the USB stick is mounted there.
(1) The icon change takes place the next time Xfe updates its internal lists, which is driven by Xfe's timers and timeout values, and thus can take a short while.
(2) Xfe's source code special-cases "proc" filesystems (usually mounted on /proc). I do not know why, so the patch does not touch that.