I've already asked Sengir about the issue of why his Habitat Locator isn't rendering when using 32x+ textures and he doesn't know. There's also another mod called Taigore's Inventory Saver which has the same issue with a Death Compass.
To me that suggests a Forge issue, but I see nothing being thrown up in the logs so I'll leave this here to see if anyone much more clever than myself can think why it would happen.
This issue doesn't happen with the normal MC Compass when in HD.
Normal Forge 818 install launched via the MC Launcher.
FML: