Issue with Finder sidebar icons

[denneval]

I have assigned custom icons to folders on an external drive, which are visible when browsing the drive through Finder (see Figure 1), but the shortcuts to these folders in the Finder sidebar display with the default folder icon (see Figure 2). Custom icons for local folders display correctly in the sidebar, as did the external drive folders before restarting my computer; once I restarted, the icons vanished, making me a very sad panda. Anyone know how I could force Finder to display these icons?