Ok, I have checked the item id before I first made this thread. The item ids are the same. So that's not the cause as to why some rares highlight and some don't.
There are 2 main differences between your xml rares files to those from another doom rares generator.
1. FlipableAttribute (I'm not sure what this does)
2. Additional item attributes (probably used the wrong terms)
eg. Movable = false;
Weight = 10.0;
These are missing from the other generator's doom rare files.
After some testing, I've come to a conclusion that it's the Movable = false; line of code which played a part to the highlighting problem. The rares from the other generator when spawned are never locked down! So players could just grab it into their packpack without stealing it. It's like locking things down in your house, after locking it down, it doesn't highlight when you mouse over. But! It doesn't explain why Hangingleggings east still highlights and others don't. So, I think you're right, it does have something to do with Item IDs, somehow ItemID 0x13DF still highlights even when set to non-movable.
Anyway, I first thought there's some kind of bug with how xml is loading those rares.
Instead, I found the bug from the other rares generator
Well, it's all good, nothing is wrong with the doomrares from xmlspawner.
Thanks for your help Arte.
xmlspawner ftw!